1 //! Constants specific to the `f64` double-precision floating point type.
3 //! *[See also the `f64` primitive type][f64].*
5 //! Mathematically significant numbers are provided in the `consts` sub-module.
7 //! For the constants defined directly in this module
8 //! (as distinct from those defined in the `consts` sub-module),
9 //! new code should instead use the associated constants
10 //! defined directly on the `f64` type.
12 #![stable(feature = "rust1", since = "1.0.0")]
14 use crate::convert::FloatToInt;
16 use crate::intrinsics;
18 use crate::num::FpCategory;
20 /// The radix or base of the internal representation of `f64`.
21 /// Use [`f64::RADIX`] instead.
27 /// # #[allow(deprecated, deprecated_in_future)]
28 /// let r = std::f64::RADIX;
31 /// let r = f64::RADIX;
33 #[stable(feature = "rust1", since = "1.0.0")]
34 #[rustc_deprecated(since = "TBD", reason = "replaced by the `RADIX` associated constant on `f64`")]
35 pub const RADIX: u32 = f64::RADIX;
37 /// Number of significant digits in base 2.
38 /// Use [`f64::MANTISSA_DIGITS`] instead.
44 /// # #[allow(deprecated, deprecated_in_future)]
45 /// let d = std::f64::MANTISSA_DIGITS;
48 /// let d = f64::MANTISSA_DIGITS;
50 #[stable(feature = "rust1", since = "1.0.0")]
53 reason = "replaced by the `MANTISSA_DIGITS` associated constant on `f64`"
55 pub const MANTISSA_DIGITS: u32 = f64::MANTISSA_DIGITS;
57 /// Approximate number of significant digits in base 10.
58 /// Use [`f64::DIGITS`] instead.
64 /// # #[allow(deprecated, deprecated_in_future)]
65 /// let d = std::f64::DIGITS;
68 /// let d = f64::DIGITS;
70 #[stable(feature = "rust1", since = "1.0.0")]
71 #[rustc_deprecated(since = "TBD", reason = "replaced by the `DIGITS` associated constant on `f64`")]
72 pub const DIGITS: u32 = f64::DIGITS;
74 /// [Machine epsilon] value for `f64`.
75 /// Use [`f64::EPSILON`] instead.
77 /// This is the difference between `1.0` and the next larger representable number.
79 /// [Machine epsilon]: https://en.wikipedia.org/wiki/Machine_epsilon
85 /// # #[allow(deprecated, deprecated_in_future)]
86 /// let e = std::f64::EPSILON;
89 /// let e = f64::EPSILON;
91 #[stable(feature = "rust1", since = "1.0.0")]
94 reason = "replaced by the `EPSILON` associated constant on `f64`"
96 pub const EPSILON: f64 = f64::EPSILON;
98 /// Smallest finite `f64` value.
99 /// Use [`f64::MIN`] instead.
104 /// // deprecated way
105 /// # #[allow(deprecated, deprecated_in_future)]
106 /// let min = std::f64::MIN;
109 /// let min = f64::MIN;
111 #[stable(feature = "rust1", since = "1.0.0")]
112 #[rustc_deprecated(since = "TBD", reason = "replaced by the `MIN` associated constant on `f64`")]
113 pub const MIN: f64 = f64::MIN;
115 /// Smallest positive normal `f64` value.
116 /// Use [`f64::MIN_POSITIVE`] instead.
121 /// // deprecated way
122 /// # #[allow(deprecated, deprecated_in_future)]
123 /// let min = std::f64::MIN_POSITIVE;
126 /// let min = f64::MIN_POSITIVE;
128 #[stable(feature = "rust1", since = "1.0.0")]
131 reason = "replaced by the `MIN_POSITIVE` associated constant on `f64`"
133 pub const MIN_POSITIVE: f64 = f64::MIN_POSITIVE;
135 /// Largest finite `f64` value.
136 /// Use [`f64::MAX`] instead.
141 /// // deprecated way
142 /// # #[allow(deprecated, deprecated_in_future)]
143 /// let max = std::f64::MAX;
146 /// let max = f64::MAX;
148 #[stable(feature = "rust1", since = "1.0.0")]
149 #[rustc_deprecated(since = "TBD", reason = "replaced by the `MAX` associated constant on `f64`")]
150 pub const MAX: f64 = f64::MAX;
152 /// One greater than the minimum possible normal power of 2 exponent.
153 /// Use [`f64::MIN_EXP`] instead.
158 /// // deprecated way
159 /// # #[allow(deprecated, deprecated_in_future)]
160 /// let min = std::f64::MIN_EXP;
163 /// let min = f64::MIN_EXP;
165 #[stable(feature = "rust1", since = "1.0.0")]
168 reason = "replaced by the `MIN_EXP` associated constant on `f64`"
170 pub const MIN_EXP: i32 = f64::MIN_EXP;
172 /// Maximum possible power of 2 exponent.
173 /// Use [`f64::MAX_EXP`] instead.
178 /// // deprecated way
179 /// # #[allow(deprecated, deprecated_in_future)]
180 /// let max = std::f64::MAX_EXP;
183 /// let max = f64::MAX_EXP;
185 #[stable(feature = "rust1", since = "1.0.0")]
188 reason = "replaced by the `MAX_EXP` associated constant on `f64`"
190 pub const MAX_EXP: i32 = f64::MAX_EXP;
192 /// Minimum possible normal power of 10 exponent.
193 /// Use [`f64::MIN_10_EXP`] instead.
198 /// // deprecated way
199 /// # #[allow(deprecated, deprecated_in_future)]
200 /// let min = std::f64::MIN_10_EXP;
203 /// let min = f64::MIN_10_EXP;
205 #[stable(feature = "rust1", since = "1.0.0")]
208 reason = "replaced by the `MIN_10_EXP` associated constant on `f64`"
210 pub const MIN_10_EXP: i32 = f64::MIN_10_EXP;
212 /// Maximum possible power of 10 exponent.
213 /// Use [`f64::MAX_10_EXP`] instead.
218 /// // deprecated way
219 /// # #[allow(deprecated, deprecated_in_future)]
220 /// let max = std::f64::MAX_10_EXP;
223 /// let max = f64::MAX_10_EXP;
225 #[stable(feature = "rust1", since = "1.0.0")]
228 reason = "replaced by the `MAX_10_EXP` associated constant on `f64`"
230 pub const MAX_10_EXP: i32 = f64::MAX_10_EXP;
232 /// Not a Number (NaN).
233 /// Use [`f64::NAN`] instead.
238 /// // deprecated way
239 /// # #[allow(deprecated, deprecated_in_future)]
240 /// let nan = std::f64::NAN;
243 /// let nan = f64::NAN;
245 #[stable(feature = "rust1", since = "1.0.0")]
246 #[rustc_deprecated(since = "TBD", reason = "replaced by the `NAN` associated constant on `f64`")]
247 pub const NAN: f64 = f64::NAN;
250 /// Use [`f64::INFINITY`] instead.
255 /// // deprecated way
256 /// # #[allow(deprecated, deprecated_in_future)]
257 /// let inf = std::f64::INFINITY;
260 /// let inf = f64::INFINITY;
262 #[stable(feature = "rust1", since = "1.0.0")]
265 reason = "replaced by the `INFINITY` associated constant on `f64`"
267 pub const INFINITY: f64 = f64::INFINITY;
269 /// Negative infinity (−∞).
270 /// Use [`f64::NEG_INFINITY`] instead.
275 /// // deprecated way
276 /// # #[allow(deprecated, deprecated_in_future)]
277 /// let ninf = std::f64::NEG_INFINITY;
280 /// let ninf = f64::NEG_INFINITY;
282 #[stable(feature = "rust1", since = "1.0.0")]
285 reason = "replaced by the `NEG_INFINITY` associated constant on `f64`"
287 pub const NEG_INFINITY: f64 = f64::NEG_INFINITY;
289 /// Basic mathematical constants.
290 #[stable(feature = "rust1", since = "1.0.0")]
292 // FIXME: replace with mathematical constants from cmath.
294 /// Archimedes' constant (π)
295 #[stable(feature = "rust1", since = "1.0.0")]
296 pub const PI: f64 = 3.14159265358979323846264338327950288_f64;
298 /// The full circle constant (τ)
301 #[stable(feature = "tau_constant", since = "1.47.0")]
302 pub const TAU: f64 = 6.28318530717958647692528676655900577_f64;
305 #[stable(feature = "rust1", since = "1.0.0")]
306 pub const FRAC_PI_2: f64 = 1.57079632679489661923132169163975144_f64;
309 #[stable(feature = "rust1", since = "1.0.0")]
310 pub const FRAC_PI_3: f64 = 1.04719755119659774615421446109316763_f64;
313 #[stable(feature = "rust1", since = "1.0.0")]
314 pub const FRAC_PI_4: f64 = 0.785398163397448309615660845819875721_f64;
317 #[stable(feature = "rust1", since = "1.0.0")]
318 pub const FRAC_PI_6: f64 = 0.52359877559829887307710723054658381_f64;
321 #[stable(feature = "rust1", since = "1.0.0")]
322 pub const FRAC_PI_8: f64 = 0.39269908169872415480783042290993786_f64;
325 #[stable(feature = "rust1", since = "1.0.0")]
326 pub const FRAC_1_PI: f64 = 0.318309886183790671537767526745028724_f64;
329 #[stable(feature = "rust1", since = "1.0.0")]
330 pub const FRAC_2_PI: f64 = 0.636619772367581343075535053490057448_f64;
333 #[stable(feature = "rust1", since = "1.0.0")]
334 pub const FRAC_2_SQRT_PI: f64 = 1.12837916709551257389615890312154517_f64;
337 #[stable(feature = "rust1", since = "1.0.0")]
338 pub const SQRT_2: f64 = 1.41421356237309504880168872420969808_f64;
341 #[stable(feature = "rust1", since = "1.0.0")]
342 pub const FRAC_1_SQRT_2: f64 = 0.707106781186547524400844362104849039_f64;
344 /// Euler's number (e)
345 #[stable(feature = "rust1", since = "1.0.0")]
346 pub const E: f64 = 2.71828182845904523536028747135266250_f64;
348 /// log<sub>2</sub>(10)
349 #[stable(feature = "extra_log_consts", since = "1.43.0")]
350 pub const LOG2_10: f64 = 3.32192809488736234787031942948939018_f64;
352 /// log<sub>2</sub>(e)
353 #[stable(feature = "rust1", since = "1.0.0")]
354 pub const LOG2_E: f64 = 1.44269504088896340735992468100189214_f64;
356 /// log<sub>10</sub>(2)
357 #[stable(feature = "extra_log_consts", since = "1.43.0")]
358 pub const LOG10_2: f64 = 0.301029995663981195213738894724493027_f64;
360 /// log<sub>10</sub>(e)
361 #[stable(feature = "rust1", since = "1.0.0")]
362 pub const LOG10_E: f64 = 0.434294481903251827651128918916605082_f64;
365 #[stable(feature = "rust1", since = "1.0.0")]
366 pub const LN_2: f64 = 0.693147180559945309417232121458176568_f64;
369 #[stable(feature = "rust1", since = "1.0.0")]
370 pub const LN_10: f64 = 2.30258509299404568401799145468436421_f64;
375 /// The radix or base of the internal representation of `f64`.
376 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
377 pub const RADIX: u32 = 2;
379 /// Number of significant digits in base 2.
380 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
381 pub const MANTISSA_DIGITS: u32 = 53;
382 /// Approximate number of significant digits in base 10.
383 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
384 pub const DIGITS: u32 = 15;
386 /// [Machine epsilon] value for `f64`.
388 /// This is the difference between `1.0` and the next larger representable number.
390 /// [Machine epsilon]: https://en.wikipedia.org/wiki/Machine_epsilon
391 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
392 pub const EPSILON: f64 = 2.2204460492503131e-16_f64;
394 /// Smallest finite `f64` value.
395 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
396 pub const MIN: f64 = -1.7976931348623157e+308_f64;
397 /// Smallest positive normal `f64` value.
398 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
399 pub const MIN_POSITIVE: f64 = 2.2250738585072014e-308_f64;
400 /// Largest finite `f64` value.
401 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
402 pub const MAX: f64 = 1.7976931348623157e+308_f64;
404 /// One greater than the minimum possible normal power of 2 exponent.
405 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
406 pub const MIN_EXP: i32 = -1021;
407 /// Maximum possible power of 2 exponent.
408 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
409 pub const MAX_EXP: i32 = 1024;
411 /// Minimum possible normal power of 10 exponent.
412 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
413 pub const MIN_10_EXP: i32 = -307;
414 /// Maximum possible power of 10 exponent.
415 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
416 pub const MAX_10_EXP: i32 = 308;
418 /// Not a Number (NaN).
419 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
420 pub const NAN: f64 = 0.0_f64 / 0.0_f64;
422 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
423 pub const INFINITY: f64 = 1.0_f64 / 0.0_f64;
424 /// Negative infinity (−∞).
425 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
426 pub const NEG_INFINITY: f64 = -1.0_f64 / 0.0_f64;
428 /// Returns `true` if this value is `NaN`.
431 /// let nan = f64::NAN;
434 /// assert!(nan.is_nan());
435 /// assert!(!f.is_nan());
438 #[stable(feature = "rust1", since = "1.0.0")]
439 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
441 pub const fn is_nan(self) -> bool {
445 // FIXME(#50145): `abs` is publicly unavailable in libcore due to
446 // concerns about portability, so this implementation is for
447 // private use internally.
449 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
450 pub(crate) const fn abs_private(self) -> f64 {
451 // SAFETY: This transmutation is fine. Probably. For the reasons std is using it.
453 mem::transmute::<u64, f64>(mem::transmute::<f64, u64>(self) & 0x7fff_ffff_ffff_ffff)
457 /// Returns `true` if this value is positive infinity or negative infinity, and
458 /// `false` otherwise.
462 /// let inf = f64::INFINITY;
463 /// let neg_inf = f64::NEG_INFINITY;
464 /// let nan = f64::NAN;
466 /// assert!(!f.is_infinite());
467 /// assert!(!nan.is_infinite());
469 /// assert!(inf.is_infinite());
470 /// assert!(neg_inf.is_infinite());
473 #[stable(feature = "rust1", since = "1.0.0")]
474 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
476 pub const fn is_infinite(self) -> bool {
477 // Getting clever with transmutation can result in incorrect answers on some FPUs
478 // FIXME: alter the Rust <-> Rust calling convention to prevent this problem.
479 // See https://github.com/rust-lang/rust/issues/72327
480 (self == f64::INFINITY) | (self == f64::NEG_INFINITY)
483 /// Returns `true` if this number is neither infinite nor `NaN`.
487 /// let inf: f64 = f64::INFINITY;
488 /// let neg_inf: f64 = f64::NEG_INFINITY;
489 /// let nan: f64 = f64::NAN;
491 /// assert!(f.is_finite());
493 /// assert!(!nan.is_finite());
494 /// assert!(!inf.is_finite());
495 /// assert!(!neg_inf.is_finite());
498 #[stable(feature = "rust1", since = "1.0.0")]
499 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
501 pub const fn is_finite(self) -> bool {
502 // There's no need to handle NaN separately: if self is NaN,
503 // the comparison is not true, exactly as desired.
504 self.abs_private() < Self::INFINITY
507 /// Returns `true` if the number is [subnormal].
510 /// let min = f64::MIN_POSITIVE; // 2.2250738585072014e-308_f64
511 /// let max = f64::MAX;
512 /// let lower_than_min = 1.0e-308_f64;
513 /// let zero = 0.0_f64;
515 /// assert!(!min.is_subnormal());
516 /// assert!(!max.is_subnormal());
518 /// assert!(!zero.is_subnormal());
519 /// assert!(!f64::NAN.is_subnormal());
520 /// assert!(!f64::INFINITY.is_subnormal());
521 /// // Values between `0` and `min` are Subnormal.
522 /// assert!(lower_than_min.is_subnormal());
524 /// [subnormal]: https://en.wikipedia.org/wiki/Denormal_number
526 #[stable(feature = "is_subnormal", since = "1.53.0")]
527 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
529 pub const fn is_subnormal(self) -> bool {
530 matches!(self.classify(), FpCategory::Subnormal)
533 /// Returns `true` if the number is neither zero, infinite,
534 /// [subnormal], or `NaN`.
537 /// let min = f64::MIN_POSITIVE; // 2.2250738585072014e-308f64
538 /// let max = f64::MAX;
539 /// let lower_than_min = 1.0e-308_f64;
540 /// let zero = 0.0f64;
542 /// assert!(min.is_normal());
543 /// assert!(max.is_normal());
545 /// assert!(!zero.is_normal());
546 /// assert!(!f64::NAN.is_normal());
547 /// assert!(!f64::INFINITY.is_normal());
548 /// // Values between `0` and `min` are Subnormal.
549 /// assert!(!lower_than_min.is_normal());
551 /// [subnormal]: https://en.wikipedia.org/wiki/Denormal_number
553 #[stable(feature = "rust1", since = "1.0.0")]
554 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
556 pub const fn is_normal(self) -> bool {
557 matches!(self.classify(), FpCategory::Normal)
560 /// Returns the floating point category of the number. If only one property
561 /// is going to be tested, it is generally faster to use the specific
562 /// predicate instead.
565 /// use std::num::FpCategory;
567 /// let num = 12.4_f64;
568 /// let inf = f64::INFINITY;
570 /// assert_eq!(num.classify(), FpCategory::Normal);
571 /// assert_eq!(inf.classify(), FpCategory::Infinite);
573 #[stable(feature = "rust1", since = "1.0.0")]
574 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
575 pub const fn classify(self) -> FpCategory {
576 // A previous implementation tried to only use bitmask-based checks,
577 // using f64::to_bits to transmute the float to its bit repr and match on that.
578 // Unfortunately, floating point numbers can be much worse than that.
579 // This also needs to not result in recursive evaluations of f64::to_bits.
581 // On some processors, in some cases, LLVM will "helpfully" lower floating point ops,
582 // in spite of a request for them using f32 and f64, to things like x87 operations.
583 // These have an f64's mantissa, but can have a larger than normal exponent.
584 // FIXME(jubilee): Using x87 operations is never necessary in order to function
585 // on x86 processors for Rust-to-Rust calls, so this issue should not happen.
586 // Code generation should be adjusted to use non-C calling conventions, avoiding this.
588 // Thus, a value may compare unequal to infinity, despite having a "full" exponent mask.
589 // And it may not be NaN, as it can simply be an "overextended" finite value.
593 // However, std can't simply compare to zero to check for zero, either,
594 // as correctness requires avoiding equality tests that may be Subnormal == -0.0
595 // because it may be wrong under "denormals are zero" and "flush to zero" modes.
596 // Most of std's targets don't use those, but they are used for thumbv7neon.
597 // So, this does use bitpattern matching for the rest.
599 // SAFETY: f64 to u64 is fine. Usually.
600 // If control flow has gotten this far, the value is definitely in one of the categories
601 // that f64::partial_classify can correctly analyze.
602 unsafe { f64::partial_classify(self) }
606 // This doesn't actually return a right answer for NaN on purpose,
607 // seeing as how it cannot correctly discern between a floating point NaN,
608 // and some normal floating point numbers truncated from an x87 FPU.
609 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
610 const unsafe fn partial_classify(self) -> FpCategory {
611 const EXP_MASK: u64 = 0x7ff0000000000000;
612 const MAN_MASK: u64 = 0x000fffffffffffff;
614 // SAFETY: The caller is not asking questions for which this will tell lies.
615 let b = unsafe { mem::transmute::<f64, u64>(self) };
616 match (b & MAN_MASK, b & EXP_MASK) {
617 (0, EXP_MASK) => FpCategory::Infinite,
618 (0, 0) => FpCategory::Zero,
619 (_, 0) => FpCategory::Subnormal,
620 _ => FpCategory::Normal,
624 // This operates on bits, and only bits, so it can ignore concerns about weird FPUs.
625 // FIXME(jubilee): In a just world, this would be the entire impl for classify,
626 // plus a transmute. We do not live in a just world, but we can make it more so.
627 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
628 const fn classify_bits(b: u64) -> FpCategory {
629 const EXP_MASK: u64 = 0x7ff0000000000000;
630 const MAN_MASK: u64 = 0x000fffffffffffff;
632 match (b & MAN_MASK, b & EXP_MASK) {
633 (0, EXP_MASK) => FpCategory::Infinite,
634 (_, EXP_MASK) => FpCategory::Nan,
635 (0, 0) => FpCategory::Zero,
636 (_, 0) => FpCategory::Subnormal,
637 _ => FpCategory::Normal,
641 /// Returns `true` if `self` has a positive sign, including `+0.0`, `NaN`s with
642 /// positive sign bit and positive infinity.
646 /// let g = -7.0_f64;
648 /// assert!(f.is_sign_positive());
649 /// assert!(!g.is_sign_positive());
652 #[stable(feature = "rust1", since = "1.0.0")]
653 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
655 pub const fn is_sign_positive(self) -> bool {
656 !self.is_sign_negative()
660 #[stable(feature = "rust1", since = "1.0.0")]
661 #[rustc_deprecated(since = "1.0.0", reason = "renamed to is_sign_positive")]
664 pub fn is_positive(self) -> bool {
665 self.is_sign_positive()
668 /// Returns `true` if `self` has a negative sign, including `-0.0`, `NaN`s with
669 /// negative sign bit and negative infinity.
673 /// let g = -7.0_f64;
675 /// assert!(!f.is_sign_negative());
676 /// assert!(g.is_sign_negative());
679 #[stable(feature = "rust1", since = "1.0.0")]
680 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
682 pub const fn is_sign_negative(self) -> bool {
683 // IEEE754 says: isSignMinus(x) is true if and only if x has negative sign. isSignMinus
684 // applies to zeros and NaNs as well.
685 // SAFETY: This is just transmuting to get the sign bit, it's fine.
686 unsafe { mem::transmute::<f64, u64>(self) & 0x8000_0000_0000_0000 != 0 }
690 #[stable(feature = "rust1", since = "1.0.0")]
691 #[rustc_deprecated(since = "1.0.0", reason = "renamed to is_sign_negative")]
694 pub fn is_negative(self) -> bool {
695 self.is_sign_negative()
698 /// Takes the reciprocal (inverse) of a number, `1/x`.
702 /// let abs_difference = (x.recip() - (1.0 / x)).abs();
704 /// assert!(abs_difference < 1e-10);
706 #[must_use = "this returns the result of the operation, without modifying the original"]
707 #[stable(feature = "rust1", since = "1.0.0")]
709 pub fn recip(self) -> f64 {
713 /// Converts radians to degrees.
716 /// let angle = std::f64::consts::PI;
718 /// let abs_difference = (angle.to_degrees() - 180.0).abs();
720 /// assert!(abs_difference < 1e-10);
722 #[must_use = "this returns the result of the operation, \
723 without modifying the original"]
724 #[stable(feature = "rust1", since = "1.0.0")]
726 pub fn to_degrees(self) -> f64 {
727 // The division here is correctly rounded with respect to the true
728 // value of 180/π. (This differs from f32, where a constant must be
729 // used to ensure a correctly rounded result.)
730 self * (180.0f64 / consts::PI)
733 /// Converts degrees to radians.
736 /// let angle = 180.0_f64;
738 /// let abs_difference = (angle.to_radians() - std::f64::consts::PI).abs();
740 /// assert!(abs_difference < 1e-10);
742 #[must_use = "this returns the result of the operation, \
743 without modifying the original"]
744 #[stable(feature = "rust1", since = "1.0.0")]
746 pub fn to_radians(self) -> f64 {
747 let value: f64 = consts::PI;
748 self * (value / 180.0)
751 /// Returns the maximum of the two numbers.
753 /// Follows the IEEE-754 2008 semantics for maxNum, except for handling of signaling NaNs.
754 /// This matches the behavior of libm’s fmax.
760 /// assert_eq!(x.max(y), y);
763 /// If one of the arguments is NaN, then the other argument is returned.
764 #[must_use = "this returns the result of the comparison, without modifying either input"]
765 #[stable(feature = "rust1", since = "1.0.0")]
767 pub fn max(self, other: f64) -> f64 {
768 intrinsics::maxnumf64(self, other)
771 /// Returns the minimum of the two numbers.
773 /// Follows the IEEE-754 2008 semantics for minNum, except for handling of signaling NaNs.
774 /// This matches the behavior of libm’s fmin.
780 /// assert_eq!(x.min(y), x);
783 /// If one of the arguments is NaN, then the other argument is returned.
784 #[must_use = "this returns the result of the comparison, without modifying either input"]
785 #[stable(feature = "rust1", since = "1.0.0")]
787 pub fn min(self, other: f64) -> f64 {
788 intrinsics::minnumf64(self, other)
791 /// Returns the maximum of the two numbers, propagating NaNs.
793 /// This returns NaN when *either* argument is NaN, as opposed to
794 /// [`f64::max`] which only returns NaN when *both* arguments are NaN.
797 /// #![feature(float_minimum_maximum)]
801 /// assert_eq!(x.maximum(y), y);
802 /// assert!(x.maximum(f64::NAN).is_nan());
805 /// If one of the arguments is NaN, then NaN is returned. Otherwise this returns the greater
806 /// of the two numbers. For this operation, -0.0 is considered to be less than +0.0.
807 /// Note that this follows the semantics specified in IEEE 754-2019.
808 #[must_use = "this returns the result of the comparison, without modifying either input"]
809 #[unstable(feature = "float_minimum_maximum", issue = "91079")]
811 pub fn maximum(self, other: f64) -> f64 {
814 } else if other > self {
816 } else if self == other {
817 if self.is_sign_positive() && other.is_sign_negative() { self } else { other }
823 /// Returns the minimum of the two numbers, propagating NaNs.
825 /// This returns NaN when *either* argument is NaN, as opposed to
826 /// [`f64::min`] which only returns NaN when *both* arguments are NaN.
829 /// #![feature(float_minimum_maximum)]
833 /// assert_eq!(x.minimum(y), x);
834 /// assert!(x.minimum(f64::NAN).is_nan());
837 /// If one of the arguments is NaN, then NaN is returned. Otherwise this returns the lesser
838 /// of the two numbers. For this operation, -0.0 is considered to be less than +0.0.
839 /// Note that this follows the semantics specified in IEEE 754-2019.
840 #[must_use = "this returns the result of the comparison, without modifying either input"]
841 #[unstable(feature = "float_minimum_maximum", issue = "91079")]
843 pub fn minimum(self, other: f64) -> f64 {
846 } else if other < self {
848 } else if self == other {
849 if self.is_sign_negative() && other.is_sign_positive() { self } else { other }
855 /// Rounds toward zero and converts to any primitive integer type,
856 /// assuming that the value is finite and fits in that type.
859 /// let value = 4.6_f64;
860 /// let rounded = unsafe { value.to_int_unchecked::<u16>() };
861 /// assert_eq!(rounded, 4);
863 /// let value = -128.9_f64;
864 /// let rounded = unsafe { value.to_int_unchecked::<i8>() };
865 /// assert_eq!(rounded, i8::MIN);
873 /// * Not be infinite
874 /// * Be representable in the return type `Int`, after truncating off its fractional part
875 #[must_use = "this returns the result of the operation, \
876 without modifying the original"]
877 #[stable(feature = "float_approx_unchecked_to", since = "1.44.0")]
879 pub unsafe fn to_int_unchecked<Int>(self) -> Int
881 Self: FloatToInt<Int>,
883 // SAFETY: the caller must uphold the safety contract for
884 // `FloatToInt::to_int_unchecked`.
885 unsafe { FloatToInt::<Int>::to_int_unchecked(self) }
888 /// Raw transmutation to `u64`.
890 /// This is currently identical to `transmute::<f64, u64>(self)` on all platforms.
892 /// See [`from_bits`](Self::from_bits) for some discussion of the
893 /// portability of this operation (there are almost no issues).
895 /// Note that this function is distinct from `as` casting, which attempts to
896 /// preserve the *numeric* value, and not the bitwise value.
901 /// assert!((1f64).to_bits() != 1f64 as u64); // to_bits() is not casting!
902 /// assert_eq!((12.5f64).to_bits(), 0x4029000000000000);
905 #[must_use = "this returns the result of the operation, \
906 without modifying the original"]
907 #[stable(feature = "float_bits_conv", since = "1.20.0")]
908 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
910 pub const fn to_bits(self) -> u64 {
911 // SAFETY: `u64` is a plain old datatype so we can always transmute to it.
914 // See the SAFETY comment in f64::from_bits for more.
915 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
916 const fn ct_f64_to_u64(ct: f64) -> u64 {
917 match ct.classify() {
919 panic!("const-eval error: cannot use f64::to_bits on a NaN")
921 FpCategory::Subnormal => {
922 panic!("const-eval error: cannot use f64::to_bits on a subnormal number")
924 FpCategory::Infinite =>
925 // SAFETY: Infinity per se is fine
926 unsafe { mem::transmute::<f64, u64>(ct) },
927 FpCategory::Zero | FpCategory::Normal => {
928 // SAFETY: We have a normal floating point number. Now we transmute, i.e. do a bitcopy.
929 let bits: u64 = unsafe { mem::transmute::<f64, u64>(ct) };
930 // Let's doublecheck to make sure it wasn't a weird float by truncating it.
931 if (bits >> 52) & 0x7FF == 0x7FF {
933 "const-eval error: an unusually large x87 floating point value should not leak into const eval"
940 // SAFETY: `u64` is a plain old datatype so we can always... uh...
941 // ...look, just pretend you forgot what you just read.
942 // Stability concerns.
943 let rt_f64_to_u64 = |rt| unsafe { mem::transmute::<f64, u64>(rt) };
944 // SAFETY: We use internal implementations that either always work or fail at compile time.
945 unsafe { intrinsics::const_eval_select((self,), ct_f64_to_u64, rt_f64_to_u64) }
948 /// Raw transmutation from `u64`.
950 /// This is currently identical to `transmute::<u64, f64>(v)` on all platforms.
951 /// It turns out this is incredibly portable, for two reasons:
953 /// * Floats and Ints have the same endianness on all supported platforms.
954 /// * IEEE-754 very precisely specifies the bit layout of floats.
956 /// However there is one caveat: prior to the 2008 version of IEEE-754, how
957 /// to interpret the NaN signaling bit wasn't actually specified. Most platforms
958 /// (notably x86 and ARM) picked the interpretation that was ultimately
959 /// standardized in 2008, but some didn't (notably MIPS). As a result, all
960 /// signaling NaNs on MIPS are quiet NaNs on x86, and vice-versa.
962 /// Rather than trying to preserve signaling-ness cross-platform, this
963 /// implementation favors preserving the exact bits. This means that
964 /// any payloads encoded in NaNs will be preserved even if the result of
965 /// this method is sent over the network from an x86 machine to a MIPS one.
967 /// If the results of this method are only manipulated by the same
968 /// architecture that produced them, then there is no portability concern.
970 /// If the input isn't NaN, then there is no portability concern.
972 /// If you don't care about signaling-ness (very likely), then there is no
973 /// portability concern.
975 /// Note that this function is distinct from `as` casting, which attempts to
976 /// preserve the *numeric* value, and not the bitwise value.
981 /// let v = f64::from_bits(0x4029000000000000);
982 /// assert_eq!(v, 12.5);
984 #[stable(feature = "float_bits_conv", since = "1.20.0")]
985 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
988 pub const fn from_bits(v: u64) -> Self {
989 // It turns out the safety issues with sNaN were overblown! Hooray!
990 // SAFETY: `u64` is a plain old datatype so we can always transmute from it
993 // It turns out that at runtime, it is possible for a floating point number
994 // to be subject to floating point modes that alter nonzero subnormal numbers
995 // to zero on reads and writes, aka "denormals are zero" and "flush to zero".
996 // This is not a problem usually, but at least one tier2 platform for Rust
997 // actually exhibits an FTZ behavior by default: thumbv7neon
998 // aka "the Neon FPU in AArch32 state"
1000 // Even with this, not all instructions exhibit the FTZ behaviors on thumbv7neon,
1001 // so this should load the same bits if LLVM emits the "correct" instructions,
1002 // but LLVM sometimes makes interesting choices about float optimization,
1003 // and other FPUs may do similar. Thus, it is wise to indulge luxuriously in caution.
1005 // In addition, on x86 targets with SSE or SSE2 disabled and the x87 FPU enabled,
1006 // i.e. not soft-float, the way Rust does parameter passing can actually alter
1007 // a number that is "not infinity" to have the same exponent as infinity,
1008 // in a slightly unpredictable manner.
1010 // And, of course evaluating to a NaN value is fairly nondeterministic.
1011 // More precisely: when NaN should be returned is knowable, but which NaN?
1012 // So far that's defined by a combination of LLVM and the CPU, not Rust.
1013 // This function, however, allows observing the bitstring of a NaN,
1014 // thus introspection on CTFE.
1016 // In order to preserve, at least for the moment, const-to-runtime equivalence,
1017 // reject any of these possible situations from happening.
1018 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
1019 const fn ct_u64_to_f64(ct: u64) -> f64 {
1020 match f64::classify_bits(ct) {
1021 FpCategory::Subnormal => {
1022 panic!("const-eval error: cannot use f64::from_bits on a subnormal number");
1024 FpCategory::Nan => {
1025 panic!("const-eval error: cannot use f64::from_bits on NaN");
1027 // SAFETY: It's not a frumious number
1028 _ => unsafe { mem::transmute::<u64, f64>(ct) },
1031 // SAFETY: `u64` is a plain old datatype so we can always... uh...
1032 // ...look, just pretend you forgot what you just read.
1033 // Stability concerns.
1034 let rt_u64_to_f64 = |rt| unsafe { mem::transmute::<u64, f64>(rt) };
1035 // SAFETY: We use internal implementations that either always work or fail at compile time.
1036 unsafe { intrinsics::const_eval_select((v,), ct_u64_to_f64, rt_u64_to_f64) }
1039 /// Return the memory representation of this floating point number as a byte array in
1040 /// big-endian (network) byte order.
1045 /// let bytes = 12.5f64.to_be_bytes();
1046 /// assert_eq!(bytes, [0x40, 0x29, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]);
1048 #[must_use = "this returns the result of the operation, \
1049 without modifying the original"]
1050 #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
1051 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
1053 pub const fn to_be_bytes(self) -> [u8; 8] {
1054 self.to_bits().to_be_bytes()
1057 /// Return the memory representation of this floating point number as a byte array in
1058 /// little-endian byte order.
1063 /// let bytes = 12.5f64.to_le_bytes();
1064 /// assert_eq!(bytes, [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x29, 0x40]);
1066 #[must_use = "this returns the result of the operation, \
1067 without modifying the original"]
1068 #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
1069 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
1071 pub const fn to_le_bytes(self) -> [u8; 8] {
1072 self.to_bits().to_le_bytes()
1075 /// Return the memory representation of this floating point number as a byte array in
1076 /// native byte order.
1078 /// As the target platform's native endianness is used, portable code
1079 /// should use [`to_be_bytes`] or [`to_le_bytes`], as appropriate, instead.
1081 /// [`to_be_bytes`]: f64::to_be_bytes
1082 /// [`to_le_bytes`]: f64::to_le_bytes
1087 /// let bytes = 12.5f64.to_ne_bytes();
1090 /// if cfg!(target_endian = "big") {
1091 /// [0x40, 0x29, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]
1093 /// [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x29, 0x40]
1097 #[must_use = "this returns the result of the operation, \
1098 without modifying the original"]
1099 #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
1100 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
1102 pub const fn to_ne_bytes(self) -> [u8; 8] {
1103 self.to_bits().to_ne_bytes()
1106 /// Create a floating point value from its representation as a byte array in big endian.
1111 /// let value = f64::from_be_bytes([0x40, 0x29, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]);
1112 /// assert_eq!(value, 12.5);
1114 #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
1115 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
1118 pub const fn from_be_bytes(bytes: [u8; 8]) -> Self {
1119 Self::from_bits(u64::from_be_bytes(bytes))
1122 /// Create a floating point value from its representation as a byte array in little endian.
1127 /// let value = f64::from_le_bytes([0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x29, 0x40]);
1128 /// assert_eq!(value, 12.5);
1130 #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
1131 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
1134 pub const fn from_le_bytes(bytes: [u8; 8]) -> Self {
1135 Self::from_bits(u64::from_le_bytes(bytes))
1138 /// Create a floating point value from its representation as a byte array in native endian.
1140 /// As the target platform's native endianness is used, portable code
1141 /// likely wants to use [`from_be_bytes`] or [`from_le_bytes`], as
1142 /// appropriate instead.
1144 /// [`from_be_bytes`]: f64::from_be_bytes
1145 /// [`from_le_bytes`]: f64::from_le_bytes
1150 /// let value = f64::from_ne_bytes(if cfg!(target_endian = "big") {
1151 /// [0x40, 0x29, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]
1153 /// [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x29, 0x40]
1155 /// assert_eq!(value, 12.5);
1157 #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
1158 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
1161 pub const fn from_ne_bytes(bytes: [u8; 8]) -> Self {
1162 Self::from_bits(u64::from_ne_bytes(bytes))
1165 /// Return the ordering between `self` and `other`.
1167 /// Unlike the standard partial comparison between floating point numbers,
1168 /// this comparison always produces an ordering in accordance to
1169 /// the `totalOrder` predicate as defined in the IEEE 754 (2008 revision)
1170 /// floating point standard. The values are ordered in the following sequence:
1172 /// - negative quiet NaN
1173 /// - negative signaling NaN
1174 /// - negative infinity
1175 /// - negative numbers
1176 /// - negative subnormal numbers
1179 /// - positive subnormal numbers
1180 /// - positive numbers
1181 /// - positive infinity
1182 /// - positive signaling NaN
1183 /// - positive quiet NaN.
1185 /// The ordering established by this function does not always agree with the
1186 /// [`PartialOrd`] and [`PartialEq`] implementations of `f64`. For example,
1187 /// they consider negative and positive zero equal, while `total_cmp`
1190 /// The interpretation of the signaling NaN bit follows the definition in
1191 /// the IEEE 754 standard, which may not match the interpretation by some of
1192 /// the older, non-conformant (e.g. MIPS) hardware implementations.
1197 /// struct GoodBoy {
1202 /// let mut bois = vec![
1203 /// GoodBoy { name: "Pucci".to_owned(), weight: 0.1 },
1204 /// GoodBoy { name: "Woofer".to_owned(), weight: 99.0 },
1205 /// GoodBoy { name: "Yapper".to_owned(), weight: 10.0 },
1206 /// GoodBoy { name: "Chonk".to_owned(), weight: f64::INFINITY },
1207 /// GoodBoy { name: "Abs. Unit".to_owned(), weight: f64::NAN },
1208 /// GoodBoy { name: "Floaty".to_owned(), weight: -5.0 },
1211 /// bois.sort_by(|a, b| a.weight.total_cmp(&b.weight));
1212 /// # assert!(bois.into_iter().map(|b| b.weight)
1213 /// # .zip([-5.0, 0.1, 10.0, 99.0, f64::INFINITY, f64::NAN].iter())
1214 /// # .all(|(a, b)| a.to_bits() == b.to_bits()))
1216 #[stable(feature = "total_cmp", since = "1.62.0")]
1219 pub fn total_cmp(&self, other: &Self) -> crate::cmp::Ordering {
1220 let mut left = self.to_bits() as i64;
1221 let mut right = other.to_bits() as i64;
1223 // In case of negatives, flip all the bits except the sign
1224 // to achieve a similar layout as two's complement integers
1226 // Why does this work? IEEE 754 floats consist of three fields:
1227 // Sign bit, exponent and mantissa. The set of exponent and mantissa
1228 // fields as a whole have the property that their bitwise order is
1229 // equal to the numeric magnitude where the magnitude is defined.
1230 // The magnitude is not normally defined on NaN values, but
1231 // IEEE 754 totalOrder defines the NaN values also to follow the
1232 // bitwise order. This leads to order explained in the doc comment.
1233 // However, the representation of magnitude is the same for negative
1234 // and positive numbers – only the sign bit is different.
1235 // To easily compare the floats as signed integers, we need to
1236 // flip the exponent and mantissa bits in case of negative numbers.
1237 // We effectively convert the numbers to "two's complement" form.
1239 // To do the flipping, we construct a mask and XOR against it.
1240 // We branchlessly calculate an "all-ones except for the sign bit"
1241 // mask from negative-signed values: right shifting sign-extends
1242 // the integer, so we "fill" the mask with sign bits, and then
1243 // convert to unsigned to push one more zero bit.
1244 // On positive values, the mask is all zeros, so it's a no-op.
1245 left ^= (((left >> 63) as u64) >> 1) as i64;
1246 right ^= (((right >> 63) as u64) >> 1) as i64;
1251 /// Restrict a value to a certain interval unless it is NaN.
1253 /// Returns `max` if `self` is greater than `max`, and `min` if `self` is
1254 /// less than `min`. Otherwise this returns `self`.
1256 /// Note that this function returns NaN if the initial value was NaN as
1261 /// Panics if `min > max`, `min` is NaN, or `max` is NaN.
1266 /// assert!((-3.0f64).clamp(-2.0, 1.0) == -2.0);
1267 /// assert!((0.0f64).clamp(-2.0, 1.0) == 0.0);
1268 /// assert!((2.0f64).clamp(-2.0, 1.0) == 1.0);
1269 /// assert!((f64::NAN).clamp(-2.0, 1.0).is_nan());
1271 #[must_use = "method returns a new number and does not mutate the original value"]
1272 #[stable(feature = "clamp", since = "1.50.0")]
1274 pub fn clamp(self, min: f64, max: f64) -> f64 {
1275 assert!(min <= max);