1 //! This module provides constants which are specific to the implementation
2 //! of the `f64` floating point data type.
4 //! *[See also the `f64` primitive type](../../std/primitive.f64.html).*
6 //! Mathematically significant numbers are provided in the `consts` sub-module.
8 //! Although using these constants won’t cause compilation warnings,
9 //! new code should use the associated constants directly on the primitive type.
11 #![stable(feature = "rust1", since = "1.0.0")]
13 use crate::convert::FloatToInt;
15 use crate::intrinsics;
17 use crate::num::FpCategory;
19 /// The radix or base of the internal representation of `f64`.
20 /// Use [`f64::RADIX`](../../std/primitive.f64.html#associatedconstant.RADIX) instead.
26 /// let r = std::f64::RADIX;
29 /// let r = f64::RADIX;
31 #[stable(feature = "rust1", since = "1.0.0")]
32 pub const RADIX: u32 = f64::RADIX;
34 /// Number of significant digits in base 2.
35 /// Use [`f64::MANTISSA_DIGITS`](../../std/primitive.f64.html#associatedconstant.MANTISSA_DIGITS) instead.
41 /// let d = std::f64::MANTISSA_DIGITS;
44 /// let d = f64::MANTISSA_DIGITS;
46 #[stable(feature = "rust1", since = "1.0.0")]
47 pub const MANTISSA_DIGITS: u32 = f64::MANTISSA_DIGITS;
49 /// Approximate number of significant digits in base 10.
50 /// Use [`f64::DIGITS`](../../std/primitive.f64.html#associatedconstant.DIGITS) instead.
56 /// let d = std::f64::DIGITS;
59 /// let d = f64::DIGITS;
61 #[stable(feature = "rust1", since = "1.0.0")]
62 pub const DIGITS: u32 = f64::DIGITS;
64 /// [Machine epsilon] value for `f64`.
65 /// Use [`f64::EPSILON`](../../std/primitive.f64.html#associatedconstant.EPSILON) instead.
67 /// This is the difference between `1.0` and the next larger representable number.
69 /// [Machine epsilon]: https://en.wikipedia.org/wiki/Machine_epsilon
75 /// let e = std::f64::EPSILON;
78 /// let e = f64::EPSILON;
80 #[stable(feature = "rust1", since = "1.0.0")]
81 pub const EPSILON: f64 = f64::EPSILON;
83 /// Smallest finite `f64` value.
84 /// Use [`f64::MIN`](../../std/primitive.f64.html#associatedconstant.MIN) instead.
90 /// let min = std::f64::MIN;
93 /// let min = f64::MIN;
95 #[stable(feature = "rust1", since = "1.0.0")]
96 pub const MIN: f64 = f64::MIN;
98 /// Smallest positive normal `f64` value.
99 /// Use [`f64::MIN_POSITIVE`](../../std/primitive.f64.html#associatedconstant.MIN_POSITIVE) instead.
104 /// // deprecated way
105 /// let min = std::f64::MIN_POSITIVE;
108 /// let min = f64::MIN_POSITIVE;
110 #[stable(feature = "rust1", since = "1.0.0")]
111 pub const MIN_POSITIVE: f64 = f64::MIN_POSITIVE;
113 /// Largest finite `f64` value.
114 /// Use [`f64::MAX`](../../std/primitive.f64.html#associatedconstant.MAX) instead.
119 /// // deprecated way
120 /// let max = std::f64::MAX;
123 /// let max = f64::MAX;
125 #[stable(feature = "rust1", since = "1.0.0")]
126 pub const MAX: f64 = f64::MAX;
128 /// One greater than the minimum possible normal power of 2 exponent.
129 /// Use [`f64::MIN_EXP`](../../std/primitive.f64.html#associatedconstant.MIN_EXP) instead.
134 /// // deprecated way
135 /// let min = std::f64::MIN_EXP;
138 /// let min = f64::MIN_EXP;
140 #[stable(feature = "rust1", since = "1.0.0")]
141 pub const MIN_EXP: i32 = f64::MIN_EXP;
143 /// Maximum possible power of 2 exponent.
144 /// Use [`f64::MAX_EXP`](../../std/primitive.f64.html#associatedconstant.MAX_EXP) instead.
149 /// // deprecated way
150 /// let max = std::f64::MAX_EXP;
153 /// let max = f64::MAX_EXP;
155 #[stable(feature = "rust1", since = "1.0.0")]
156 pub const MAX_EXP: i32 = f64::MAX_EXP;
158 /// Minimum possible normal power of 10 exponent.
159 /// Use [`f64::MIN_10_EXP`](../../std/primitive.f64.html#associatedconstant.MIN_10_EXP) instead.
164 /// // deprecated way
165 /// let min = std::f64::MIN_10_EXP;
168 /// let min = f64::MIN_10_EXP;
170 #[stable(feature = "rust1", since = "1.0.0")]
171 pub const MIN_10_EXP: i32 = f64::MIN_10_EXP;
173 /// Maximum possible power of 10 exponent.
174 /// Use [`f64::MAX_10_EXP`](../../std/primitive.f64.html#associatedconstant.MAX_10_EXP) instead.
179 /// // deprecated way
180 /// let max = std::f64::MAX_10_EXP;
183 /// let max = f64::MAX_10_EXP;
185 #[stable(feature = "rust1", since = "1.0.0")]
186 pub const MAX_10_EXP: i32 = f64::MAX_10_EXP;
188 /// Not a Number (NaN).
189 /// Use [`f64::NAN`](../../std/primitive.f64.html#associatedconstant.NAN) instead.
194 /// // deprecated way
195 /// let nan = std::f64::NAN;
198 /// let nan = f64::NAN;
200 #[stable(feature = "rust1", since = "1.0.0")]
201 pub const NAN: f64 = f64::NAN;
204 /// Use [`f64::INFINITY`](../../std/primitive.f64.html#associatedconstant.INFINITY) instead.
209 /// // deprecated way
210 /// let inf = std::f64::INFINITY;
213 /// let inf = f64::INFINITY;
215 #[stable(feature = "rust1", since = "1.0.0")]
216 pub const INFINITY: f64 = f64::INFINITY;
218 /// Negative infinity (−∞).
219 /// Use [`f64::NEG_INFINITY`](../../std/primitive.f64.html#associatedconstant.NEG_INFINITY) instead.
224 /// // deprecated way
225 /// let ninf = std::f64::NEG_INFINITY;
228 /// let ninf = f64::NEG_INFINITY;
230 #[stable(feature = "rust1", since = "1.0.0")]
231 pub const NEG_INFINITY: f64 = f64::NEG_INFINITY;
233 /// Basic mathematical constants.
234 #[stable(feature = "rust1", since = "1.0.0")]
236 // FIXME: replace with mathematical constants from cmath.
238 /// Archimedes' constant (π)
239 #[stable(feature = "rust1", since = "1.0.0")]
240 pub const PI: f64 = 3.14159265358979323846264338327950288_f64;
242 /// The full circle constant (τ)
245 #[stable(feature = "tau_constant", since = "1.47.0")]
246 pub const TAU: f64 = 6.28318530717958647692528676655900577_f64;
249 #[stable(feature = "rust1", since = "1.0.0")]
250 pub const FRAC_PI_2: f64 = 1.57079632679489661923132169163975144_f64;
253 #[stable(feature = "rust1", since = "1.0.0")]
254 pub const FRAC_PI_3: f64 = 1.04719755119659774615421446109316763_f64;
257 #[stable(feature = "rust1", since = "1.0.0")]
258 pub const FRAC_PI_4: f64 = 0.785398163397448309615660845819875721_f64;
261 #[stable(feature = "rust1", since = "1.0.0")]
262 pub const FRAC_PI_6: f64 = 0.52359877559829887307710723054658381_f64;
265 #[stable(feature = "rust1", since = "1.0.0")]
266 pub const FRAC_PI_8: f64 = 0.39269908169872415480783042290993786_f64;
269 #[stable(feature = "rust1", since = "1.0.0")]
270 pub const FRAC_1_PI: f64 = 0.318309886183790671537767526745028724_f64;
273 #[stable(feature = "rust1", since = "1.0.0")]
274 pub const FRAC_2_PI: f64 = 0.636619772367581343075535053490057448_f64;
277 #[stable(feature = "rust1", since = "1.0.0")]
278 pub const FRAC_2_SQRT_PI: f64 = 1.12837916709551257389615890312154517_f64;
281 #[stable(feature = "rust1", since = "1.0.0")]
282 pub const SQRT_2: f64 = 1.41421356237309504880168872420969808_f64;
285 #[stable(feature = "rust1", since = "1.0.0")]
286 pub const FRAC_1_SQRT_2: f64 = 0.707106781186547524400844362104849039_f64;
288 /// Euler's number (e)
289 #[stable(feature = "rust1", since = "1.0.0")]
290 pub const E: f64 = 2.71828182845904523536028747135266250_f64;
292 /// log<sub>2</sub>(10)
293 #[stable(feature = "extra_log_consts", since = "1.43.0")]
294 pub const LOG2_10: f64 = 3.32192809488736234787031942948939018_f64;
296 /// log<sub>2</sub>(e)
297 #[stable(feature = "rust1", since = "1.0.0")]
298 pub const LOG2_E: f64 = 1.44269504088896340735992468100189214_f64;
300 /// log<sub>10</sub>(2)
301 #[stable(feature = "extra_log_consts", since = "1.43.0")]
302 pub const LOG10_2: f64 = 0.301029995663981195213738894724493027_f64;
304 /// log<sub>10</sub>(e)
305 #[stable(feature = "rust1", since = "1.0.0")]
306 pub const LOG10_E: f64 = 0.434294481903251827651128918916605082_f64;
309 #[stable(feature = "rust1", since = "1.0.0")]
310 pub const LN_2: f64 = 0.693147180559945309417232121458176568_f64;
313 #[stable(feature = "rust1", since = "1.0.0")]
314 pub const LN_10: f64 = 2.30258509299404568401799145468436421_f64;
320 /// The radix or base of the internal representation of `f64`.
321 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
322 pub const RADIX: u32 = 2;
324 /// Number of significant digits in base 2.
325 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
326 pub const MANTISSA_DIGITS: u32 = 53;
327 /// Approximate number of significant digits in base 10.
328 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
329 pub const DIGITS: u32 = 15;
331 /// [Machine epsilon] value for `f64`.
333 /// This is the difference between `1.0` and the next larger representable number.
335 /// [Machine epsilon]: https://en.wikipedia.org/wiki/Machine_epsilon
336 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
337 pub const EPSILON: f64 = 2.2204460492503131e-16_f64;
339 /// Smallest finite `f64` value.
340 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
341 pub const MIN: f64 = -1.7976931348623157e+308_f64;
342 /// Smallest positive normal `f64` value.
343 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
344 pub const MIN_POSITIVE: f64 = 2.2250738585072014e-308_f64;
345 /// Largest finite `f64` value.
346 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
347 pub const MAX: f64 = 1.7976931348623157e+308_f64;
349 /// One greater than the minimum possible normal power of 2 exponent.
350 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
351 pub const MIN_EXP: i32 = -1021;
352 /// Maximum possible power of 2 exponent.
353 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
354 pub const MAX_EXP: i32 = 1024;
356 /// Minimum possible normal power of 10 exponent.
357 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
358 pub const MIN_10_EXP: i32 = -307;
359 /// Maximum possible power of 10 exponent.
360 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
361 pub const MAX_10_EXP: i32 = 308;
363 /// Not a Number (NaN).
364 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
365 pub const NAN: f64 = 0.0_f64 / 0.0_f64;
367 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
368 pub const INFINITY: f64 = 1.0_f64 / 0.0_f64;
369 /// Negative infinity (−∞).
370 #[stable(feature = "assoc_int_consts", since = "1.43.0")]
371 pub const NEG_INFINITY: f64 = -1.0_f64 / 0.0_f64;
373 /// Returns `true` if this value is `NaN`.
376 /// let nan = f64::NAN;
379 /// assert!(nan.is_nan());
380 /// assert!(!f.is_nan());
382 #[stable(feature = "rust1", since = "1.0.0")]
383 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
385 pub const fn is_nan(self) -> bool {
389 // FIXME(#50145): `abs` is publicly unavailable in libcore due to
390 // concerns about portability, so this implementation is for
391 // private use internally.
393 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
394 const fn abs_private(self) -> f64 {
395 f64::from_bits(self.to_bits() & 0x7fff_ffff_ffff_ffff)
398 /// Returns `true` if this value is positive infinity or negative infinity, and
399 /// `false` otherwise.
403 /// let inf = f64::INFINITY;
404 /// let neg_inf = f64::NEG_INFINITY;
405 /// let nan = f64::NAN;
407 /// assert!(!f.is_infinite());
408 /// assert!(!nan.is_infinite());
410 /// assert!(inf.is_infinite());
411 /// assert!(neg_inf.is_infinite());
413 #[stable(feature = "rust1", since = "1.0.0")]
414 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
416 pub const fn is_infinite(self) -> bool {
417 self.abs_private() == Self::INFINITY
420 /// Returns `true` if this number is neither infinite nor `NaN`.
424 /// let inf: f64 = f64::INFINITY;
425 /// let neg_inf: f64 = f64::NEG_INFINITY;
426 /// let nan: f64 = f64::NAN;
428 /// assert!(f.is_finite());
430 /// assert!(!nan.is_finite());
431 /// assert!(!inf.is_finite());
432 /// assert!(!neg_inf.is_finite());
434 #[stable(feature = "rust1", since = "1.0.0")]
435 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
437 pub const fn is_finite(self) -> bool {
438 // There's no need to handle NaN separately: if self is NaN,
439 // the comparison is not true, exactly as desired.
440 self.abs_private() < Self::INFINITY
443 /// Returns `true` if the number is [subnormal].
446 /// #![feature(is_subnormal)]
447 /// let min = f64::MIN_POSITIVE; // 2.2250738585072014e-308_f64
448 /// let max = f64::MAX;
449 /// let lower_than_min = 1.0e-308_f64;
450 /// let zero = 0.0_f64;
452 /// assert!(!min.is_subnormal());
453 /// assert!(!max.is_subnormal());
455 /// assert!(!zero.is_subnormal());
456 /// assert!(!f64::NAN.is_subnormal());
457 /// assert!(!f64::INFINITY.is_subnormal());
458 /// // Values between `0` and `min` are Subnormal.
459 /// assert!(lower_than_min.is_subnormal());
461 /// [subnormal]: https://en.wikipedia.org/wiki/Denormal_number
462 #[unstable(feature = "is_subnormal", issue = "79288")]
463 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
465 pub const fn is_subnormal(self) -> bool {
466 matches!(self.classify(), FpCategory::Subnormal)
469 /// Returns `true` if the number is neither zero, infinite,
470 /// [subnormal], or `NaN`.
473 /// let min = f64::MIN_POSITIVE; // 2.2250738585072014e-308f64
474 /// let max = f64::MAX;
475 /// let lower_than_min = 1.0e-308_f64;
476 /// let zero = 0.0f64;
478 /// assert!(min.is_normal());
479 /// assert!(max.is_normal());
481 /// assert!(!zero.is_normal());
482 /// assert!(!f64::NAN.is_normal());
483 /// assert!(!f64::INFINITY.is_normal());
484 /// // Values between `0` and `min` are Subnormal.
485 /// assert!(!lower_than_min.is_normal());
487 /// [subnormal]: https://en.wikipedia.org/wiki/Denormal_number
488 #[stable(feature = "rust1", since = "1.0.0")]
489 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
491 pub const fn is_normal(self) -> bool {
492 matches!(self.classify(), FpCategory::Normal)
495 /// Returns the floating point category of the number. If only one property
496 /// is going to be tested, it is generally faster to use the specific
497 /// predicate instead.
500 /// use std::num::FpCategory;
502 /// let num = 12.4_f64;
503 /// let inf = f64::INFINITY;
505 /// assert_eq!(num.classify(), FpCategory::Normal);
506 /// assert_eq!(inf.classify(), FpCategory::Infinite);
508 #[stable(feature = "rust1", since = "1.0.0")]
509 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
510 pub const fn classify(self) -> FpCategory {
511 const EXP_MASK: u64 = 0x7ff0000000000000;
512 const MAN_MASK: u64 = 0x000fffffffffffff;
514 let bits = self.to_bits();
515 match (bits & MAN_MASK, bits & EXP_MASK) {
516 (0, 0) => FpCategory::Zero,
517 (_, 0) => FpCategory::Subnormal,
518 (0, EXP_MASK) => FpCategory::Infinite,
519 (_, EXP_MASK) => FpCategory::Nan,
520 _ => FpCategory::Normal,
524 /// Returns `true` if `self` has a positive sign, including `+0.0`, `NaN`s with
525 /// positive sign bit and positive infinity.
529 /// let g = -7.0_f64;
531 /// assert!(f.is_sign_positive());
532 /// assert!(!g.is_sign_positive());
534 #[stable(feature = "rust1", since = "1.0.0")]
535 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
537 pub const fn is_sign_positive(self) -> bool {
538 !self.is_sign_negative()
541 #[stable(feature = "rust1", since = "1.0.0")]
542 #[rustc_deprecated(since = "1.0.0", reason = "renamed to is_sign_positive")]
545 pub fn is_positive(self) -> bool {
546 self.is_sign_positive()
549 /// Returns `true` if `self` has a negative sign, including `-0.0`, `NaN`s with
550 /// negative sign bit and negative infinity.
554 /// let g = -7.0_f64;
556 /// assert!(!f.is_sign_negative());
557 /// assert!(g.is_sign_negative());
559 #[stable(feature = "rust1", since = "1.0.0")]
560 #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
562 pub const fn is_sign_negative(self) -> bool {
563 self.to_bits() & 0x8000_0000_0000_0000 != 0
566 #[stable(feature = "rust1", since = "1.0.0")]
567 #[rustc_deprecated(since = "1.0.0", reason = "renamed to is_sign_negative")]
570 pub fn is_negative(self) -> bool {
571 self.is_sign_negative()
574 /// Takes the reciprocal (inverse) of a number, `1/x`.
578 /// let abs_difference = (x.recip() - (1.0 / x)).abs();
580 /// assert!(abs_difference < 1e-10);
582 #[stable(feature = "rust1", since = "1.0.0")]
584 pub fn recip(self) -> f64 {
588 /// Converts radians to degrees.
591 /// let angle = std::f64::consts::PI;
593 /// let abs_difference = (angle.to_degrees() - 180.0).abs();
595 /// assert!(abs_difference < 1e-10);
597 #[stable(feature = "rust1", since = "1.0.0")]
599 pub fn to_degrees(self) -> f64 {
600 // The division here is correctly rounded with respect to the true
601 // value of 180/π. (This differs from f32, where a constant must be
602 // used to ensure a correctly rounded result.)
603 self * (180.0f64 / consts::PI)
606 /// Converts degrees to radians.
609 /// let angle = 180.0_f64;
611 /// let abs_difference = (angle.to_radians() - std::f64::consts::PI).abs();
613 /// assert!(abs_difference < 1e-10);
615 #[stable(feature = "rust1", since = "1.0.0")]
617 pub fn to_radians(self) -> f64 {
618 let value: f64 = consts::PI;
619 self * (value / 180.0)
622 /// Returns the maximum of the two numbers.
628 /// assert_eq!(x.max(y), y);
631 /// If one of the arguments is NaN, then the other argument is returned.
632 #[stable(feature = "rust1", since = "1.0.0")]
634 pub fn max(self, other: f64) -> f64 {
635 intrinsics::maxnumf64(self, other)
638 /// Returns the minimum of the two numbers.
644 /// assert_eq!(x.min(y), x);
647 /// If one of the arguments is NaN, then the other argument is returned.
648 #[stable(feature = "rust1", since = "1.0.0")]
650 pub fn min(self, other: f64) -> f64 {
651 intrinsics::minnumf64(self, other)
654 /// Rounds toward zero and converts to any primitive integer type,
655 /// assuming that the value is finite and fits in that type.
658 /// let value = 4.6_f64;
659 /// let rounded = unsafe { value.to_int_unchecked::<u16>() };
660 /// assert_eq!(rounded, 4);
662 /// let value = -128.9_f64;
663 /// let rounded = unsafe { value.to_int_unchecked::<i8>() };
664 /// assert_eq!(rounded, i8::MIN);
672 /// * Not be infinite
673 /// * Be representable in the return type `Int`, after truncating off its fractional part
674 #[stable(feature = "float_approx_unchecked_to", since = "1.44.0")]
676 pub unsafe fn to_int_unchecked<Int>(self) -> Int
678 Self: FloatToInt<Int>,
680 // SAFETY: the caller must uphold the safety contract for
681 // `FloatToInt::to_int_unchecked`.
682 unsafe { FloatToInt::<Int>::to_int_unchecked(self) }
685 /// Raw transmutation to `u64`.
687 /// This is currently identical to `transmute::<f64, u64>(self)` on all platforms.
689 /// See `from_bits` for some discussion of the portability of this operation
690 /// (there are almost no issues).
692 /// Note that this function is distinct from `as` casting, which attempts to
693 /// preserve the *numeric* value, and not the bitwise value.
698 /// assert!((1f64).to_bits() != 1f64 as u64); // to_bits() is not casting!
699 /// assert_eq!((12.5f64).to_bits(), 0x4029000000000000);
702 #[stable(feature = "float_bits_conv", since = "1.20.0")]
703 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
705 pub const fn to_bits(self) -> u64 {
706 // SAFETY: `u64` is a plain old datatype so we can always transmute to it
707 unsafe { mem::transmute(self) }
710 /// Raw transmutation from `u64`.
712 /// This is currently identical to `transmute::<u64, f64>(v)` on all platforms.
713 /// It turns out this is incredibly portable, for two reasons:
715 /// * Floats and Ints have the same endianness on all supported platforms.
716 /// * IEEE-754 very precisely specifies the bit layout of floats.
718 /// However there is one caveat: prior to the 2008 version of IEEE-754, how
719 /// to interpret the NaN signaling bit wasn't actually specified. Most platforms
720 /// (notably x86 and ARM) picked the interpretation that was ultimately
721 /// standardized in 2008, but some didn't (notably MIPS). As a result, all
722 /// signaling NaNs on MIPS are quiet NaNs on x86, and vice-versa.
724 /// Rather than trying to preserve signaling-ness cross-platform, this
725 /// implementation favors preserving the exact bits. This means that
726 /// any payloads encoded in NaNs will be preserved even if the result of
727 /// this method is sent over the network from an x86 machine to a MIPS one.
729 /// If the results of this method are only manipulated by the same
730 /// architecture that produced them, then there is no portability concern.
732 /// If the input isn't NaN, then there is no portability concern.
734 /// If you don't care about signaling-ness (very likely), then there is no
735 /// portability concern.
737 /// Note that this function is distinct from `as` casting, which attempts to
738 /// preserve the *numeric* value, and not the bitwise value.
743 /// let v = f64::from_bits(0x4029000000000000);
744 /// assert_eq!(v, 12.5);
746 #[stable(feature = "float_bits_conv", since = "1.20.0")]
747 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
749 pub const fn from_bits(v: u64) -> Self {
750 // SAFETY: `u64` is a plain old datatype so we can always transmute from it
751 // It turns out the safety issues with sNaN were overblown! Hooray!
752 unsafe { mem::transmute(v) }
755 /// Return the memory representation of this floating point number as a byte array in
756 /// big-endian (network) byte order.
761 /// let bytes = 12.5f64.to_be_bytes();
762 /// assert_eq!(bytes, [0x40, 0x29, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]);
764 #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
765 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
767 pub const fn to_be_bytes(self) -> [u8; 8] {
768 self.to_bits().to_be_bytes()
771 /// Return the memory representation of this floating point number as a byte array in
772 /// little-endian byte order.
777 /// let bytes = 12.5f64.to_le_bytes();
778 /// assert_eq!(bytes, [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x29, 0x40]);
780 #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
781 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
783 pub const fn to_le_bytes(self) -> [u8; 8] {
784 self.to_bits().to_le_bytes()
787 /// Return the memory representation of this floating point number as a byte array in
788 /// native byte order.
790 /// As the target platform's native endianness is used, portable code
791 /// should use [`to_be_bytes`] or [`to_le_bytes`], as appropriate, instead.
793 /// [`to_be_bytes`]: #method.to_be_bytes
794 /// [`to_le_bytes`]: #method.to_le_bytes
799 /// let bytes = 12.5f64.to_ne_bytes();
802 /// if cfg!(target_endian = "big") {
803 /// [0x40, 0x29, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]
805 /// [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x29, 0x40]
809 #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
810 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
812 pub const fn to_ne_bytes(self) -> [u8; 8] {
813 self.to_bits().to_ne_bytes()
816 /// Return the memory representation of this floating point number as a byte array in
817 /// native byte order.
819 /// [`to_ne_bytes`] should be preferred over this whenever possible.
821 /// [`to_ne_bytes`]: #method.to_ne_bytes
826 /// #![feature(num_as_ne_bytes)]
827 /// let num = 12.5f64;
828 /// let bytes = num.as_ne_bytes();
831 /// if cfg!(target_endian = "big") {
832 /// &[0x40, 0x29, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]
834 /// &[0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x29, 0x40]
838 #[unstable(feature = "num_as_ne_bytes", issue = "76976")]
840 pub fn as_ne_bytes(&self) -> &[u8; 8] {
841 // SAFETY: `f64` is a plain old datatype so we can always transmute to it
842 unsafe { &*(self as *const Self as *const _) }
845 /// Create a floating point value from its representation as a byte array in big endian.
850 /// let value = f64::from_be_bytes([0x40, 0x29, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]);
851 /// assert_eq!(value, 12.5);
853 #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
854 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
856 pub const fn from_be_bytes(bytes: [u8; 8]) -> Self {
857 Self::from_bits(u64::from_be_bytes(bytes))
860 /// Create a floating point value from its representation as a byte array in little endian.
865 /// let value = f64::from_le_bytes([0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x29, 0x40]);
866 /// assert_eq!(value, 12.5);
868 #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
869 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
871 pub const fn from_le_bytes(bytes: [u8; 8]) -> Self {
872 Self::from_bits(u64::from_le_bytes(bytes))
875 /// Create a floating point value from its representation as a byte array in native endian.
877 /// As the target platform's native endianness is used, portable code
878 /// likely wants to use [`from_be_bytes`] or [`from_le_bytes`], as
879 /// appropriate instead.
881 /// [`from_be_bytes`]: #method.from_be_bytes
882 /// [`from_le_bytes`]: #method.from_le_bytes
887 /// let value = f64::from_ne_bytes(if cfg!(target_endian = "big") {
888 /// [0x40, 0x29, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]
890 /// [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x29, 0x40]
892 /// assert_eq!(value, 12.5);
894 #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
895 #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
897 pub const fn from_ne_bytes(bytes: [u8; 8]) -> Self {
898 Self::from_bits(u64::from_ne_bytes(bytes))
901 /// Returns an ordering between self and other values.
902 /// Unlike the standard partial comparison between floating point numbers,
903 /// this comparison always produces an ordering in accordance to
904 /// the totalOrder predicate as defined in IEEE 754 (2008 revision)
905 /// floating point standard. The values are ordered in following order:
906 /// - Negative quiet NaN
907 /// - Negative signaling NaN
908 /// - Negative infinity
909 /// - Negative numbers
910 /// - Negative subnormal numbers
913 /// - Positive subnormal numbers
914 /// - Positive numbers
915 /// - Positive infinity
916 /// - Positive signaling NaN
917 /// - Positive quiet NaN
919 /// Note that this function does not always agree with the [`PartialOrd`]
920 /// and [`PartialEq`] implementations of `f64`. In particular, they regard
921 /// negative and positive zero as equal, while `total_cmp` doesn't.
925 /// #![feature(total_cmp)]
931 /// let mut bois = vec![
932 /// GoodBoy { name: "Pucci".to_owned(), weight: 0.1 },
933 /// GoodBoy { name: "Woofer".to_owned(), weight: 99.0 },
934 /// GoodBoy { name: "Yapper".to_owned(), weight: 10.0 },
935 /// GoodBoy { name: "Chonk".to_owned(), weight: f64::INFINITY },
936 /// GoodBoy { name: "Abs. Unit".to_owned(), weight: f64::NAN },
937 /// GoodBoy { name: "Floaty".to_owned(), weight: -5.0 },
940 /// bois.sort_by(|a, b| a.weight.total_cmp(&b.weight));
941 /// # assert!(bois.into_iter().map(|b| b.weight)
942 /// # .zip([-5.0, 0.1, 10.0, 99.0, f64::INFINITY, f64::NAN].iter())
943 /// # .all(|(a, b)| a.to_bits() == b.to_bits()))
945 #[unstable(feature = "total_cmp", issue = "72599")]
947 pub fn total_cmp(&self, other: &Self) -> crate::cmp::Ordering {
948 let mut left = self.to_bits() as i64;
949 let mut right = other.to_bits() as i64;
951 // In case of negatives, flip all the bits except the sign
952 // to achieve a similar layout as two's complement integers
954 // Why does this work? IEEE 754 floats consist of three fields:
955 // Sign bit, exponent and mantissa. The set of exponent and mantissa
956 // fields as a whole have the property that their bitwise order is
957 // equal to the numeric magnitude where the magnitude is defined.
958 // The magnitude is not normally defined on NaN values, but
959 // IEEE 754 totalOrder defines the NaN values also to follow the
960 // bitwise order. This leads to order explained in the doc comment.
961 // However, the representation of magnitude is the same for negative
962 // and positive numbers – only the sign bit is different.
963 // To easily compare the floats as signed integers, we need to
964 // flip the exponent and mantissa bits in case of negative numbers.
965 // We effectively convert the numbers to "two's complement" form.
967 // To do the flipping, we construct a mask and XOR against it.
968 // We branchlessly calculate an "all-ones except for the sign bit"
969 // mask from negative-signed values: right shifting sign-extends
970 // the integer, so we "fill" the mask with sign bits, and then
971 // convert to unsigned to push one more zero bit.
972 // On positive values, the mask is all zeros, so it's a no-op.
973 left ^= (((left >> 63) as u64) >> 1) as i64;
974 right ^= (((right >> 63) as u64) >> 1) as i64;