1 use clippy_utils::consts::{
2 constant, constant_simple, Constant,
3 Constant::{Int, F32, F64},
5 use clippy_utils::diagnostics::span_lint_and_sugg;
6 use clippy_utils::higher;
7 use clippy_utils::{eq_expr_value, get_parent_expr, in_constant, numeric_literal, peel_blocks, sugg};
8 use if_chain::if_chain;
9 use rustc_errors::Applicability;
10 use rustc_hir::{BinOpKind, Expr, ExprKind, PathSegment, UnOp};
11 use rustc_lint::{LateContext, LateLintPass};
13 use rustc_session::{declare_lint_pass, declare_tool_lint};
14 use rustc_span::source_map::Spanned;
17 use std::f32::consts as f32_consts;
18 use std::f64::consts as f64_consts;
21 declare_clippy_lint! {
23 /// Looks for floating-point expressions that
24 /// can be expressed using built-in methods to improve accuracy
25 /// at the cost of performance.
27 /// ### Why is this bad?
28 /// Negatively impacts accuracy.
33 /// let _ = a.powf(1.0 / 3.0);
34 /// let _ = (1.0 + a).ln();
35 /// let _ = a.exp() - 1.0;
42 /// let _ = a.ln_1p();
43 /// let _ = a.exp_m1();
45 #[clippy::version = "1.43.0"]
48 "usage of imprecise floating point operations"
51 declare_clippy_lint! {
53 /// Looks for floating-point expressions that
54 /// can be expressed using built-in methods to improve both
55 /// accuracy and performance.
57 /// ### Why is this bad?
58 /// Negatively impacts accuracy and performance.
62 /// use std::f32::consts::E;
65 /// let _ = (2f32).powf(a);
66 /// let _ = E.powf(a);
67 /// let _ = a.powf(1.0 / 2.0);
68 /// let _ = a.log(2.0);
69 /// let _ = a.log(10.0);
71 /// let _ = a.powf(2.0);
72 /// let _ = a * 2.0 + 4.0;
73 /// let _ = if a < 0.0 {
78 /// let _ = if a < 0.0 {
85 /// is better expressed as
88 /// use std::f32::consts::E;
95 /// let _ = a.log10();
97 /// let _ = a.powi(2);
98 /// let _ = a.mul_add(2.0, 4.0);
100 /// let _ = -a.abs();
102 #[clippy::version = "1.43.0"]
103 pub SUBOPTIMAL_FLOPS,
105 "usage of sub-optimal floating point operations"
108 declare_lint_pass!(FloatingPointArithmetic => [
113 // Returns the specialized log method for a given base if base is constant
114 // and is one of 2, 10 and e
115 fn get_specialized_log_method(cx: &LateContext<'_>, base: &Expr<'_>) -> Option<&'static str> {
116 if let Some((value, _)) = constant(cx, cx.typeck_results(), base) {
117 if F32(2.0) == value || F64(2.0) == value {
119 } else if F32(10.0) == value || F64(10.0) == value {
120 return Some("log10");
121 } else if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
129 // Adds type suffixes and parenthesis to method receivers if necessary
130 fn prepare_receiver_sugg<'a>(cx: &LateContext<'_>, mut expr: &'a Expr<'a>) -> Sugg<'a> {
131 let mut suggestion = Sugg::hir(cx, expr, "..");
133 if let ExprKind::Unary(UnOp::Neg, inner_expr) = &expr.kind {
138 // if the expression is a float literal and it is unsuffixed then
139 // add a suffix so the suggestion is valid and unambiguous
140 if let ty::Float(float_ty) = cx.typeck_results().expr_ty(expr).kind();
141 if let ExprKind::Lit(lit) = &expr.kind;
142 if let ast::LitKind::Float(sym, ast::LitFloatType::Unsuffixed) = lit.node;
147 // Check for float literals without numbers following the decimal
148 // separator such as `2.` and adds a trailing zero
149 if sym.as_str().ends_with('.') {
157 suggestion = match suggestion {
158 Sugg::MaybeParen(_) => Sugg::MaybeParen(op),
159 _ => Sugg::NonParen(op)
164 suggestion.maybe_par()
167 fn check_log_base(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args: &[Expr<'_>]) {
168 if let Some(method) = get_specialized_log_method(cx, &args[0]) {
173 "logarithm for bases 2, 10 and e can be computed more accurately",
175 format!("{}.{}()", Sugg::hir(cx, receiver, "..").maybe_par(), method),
176 Applicability::MachineApplicable,
181 // TODO: Lint expressions of the form `(x + y).ln()` where y > 1 and
182 // suggest usage of `(x + (y - 1)).ln_1p()` instead
183 fn check_ln1p(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>) {
184 if let ExprKind::Binary(
186 node: BinOpKind::Add, ..
193 constant(cx, cx.typeck_results(), lhs),
194 constant(cx, cx.typeck_results(), rhs),
196 (Some((value, _)), _) if F32(1.0) == value || F64(1.0) == value => rhs,
197 (_, Some((value, _))) if F32(1.0) == value || F64(1.0) == value => lhs,
205 "ln(1 + x) can be computed more accurately",
207 format!("{}.ln_1p()", prepare_receiver_sugg(cx, recv)),
208 Applicability::MachineApplicable,
213 // Returns an integer if the float constant is a whole number and it can be
214 // converted to an integer without loss of precision. For now we only check
215 // ranges [-16777215, 16777216) for type f32 as whole number floats outside
216 // this range are lossy and ambiguous.
217 #[expect(clippy::cast_possible_truncation)]
218 fn get_integer_from_float_constant(value: &Constant) -> Option<i32> {
220 F32(num) if num.fract() == 0.0 => {
221 if (-16_777_215.0..16_777_216.0).contains(num) {
222 Some(num.round() as i32)
227 F64(num) if num.fract() == 0.0 => {
228 if (-2_147_483_648.0..2_147_483_648.0).contains(num) {
229 Some(num.round() as i32)
238 fn check_powf(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args: &[Expr<'_>]) {
240 if let Some((value, _)) = constant(cx, cx.typeck_results(), receiver) {
241 if let Some(method) = if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
243 } else if F32(2.0) == value || F64(2.0) == value {
252 "exponent for bases 2 and e can be computed more accurately",
254 format!("{}.{}()", prepare_receiver_sugg(cx, &args[0]), method),
255 Applicability::MachineApplicable,
261 if let Some((value, _)) = constant(cx, cx.typeck_results(), &args[0]) {
262 let (lint, help, suggestion) = if F32(1.0 / 2.0) == value || F64(1.0 / 2.0) == value {
265 "square-root of a number can be computed more efficiently and accurately",
266 format!("{}.sqrt()", Sugg::hir(cx, receiver, "..").maybe_par()),
268 } else if F32(1.0 / 3.0) == value || F64(1.0 / 3.0) == value {
271 "cube-root of a number can be computed more accurately",
272 format!("{}.cbrt()", Sugg::hir(cx, receiver, "..").maybe_par()),
274 } else if let Some(exponent) = get_integer_from_float_constant(&value) {
277 "exponentiation with integer powers can be computed more efficiently",
280 Sugg::hir(cx, receiver, "..").maybe_par(),
281 numeric_literal::format(&exponent.to_string(), None, false)
295 Applicability::MachineApplicable,
300 fn check_powi(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args: &[Expr<'_>]) {
301 if let Some((value, _)) = constant(cx, cx.typeck_results(), &args[0]) {
303 if let Some(parent) = get_parent_expr(cx, expr) {
304 if let Some(grandparent) = get_parent_expr(cx, parent) {
305 if let ExprKind::MethodCall(PathSegment { ident: method_name, .. }, receiver, ..) = grandparent.kind
307 if method_name.as_str() == "sqrt" && detect_hypot(cx, receiver).is_some() {
313 if let ExprKind::Binary(
315 node: BinOpKind::Add, ..
321 let other_addend = if lhs.hir_id == expr.hir_id { rhs } else { lhs };
327 "multiply and add expressions can be calculated more efficiently and accurately",
330 "{}.mul_add({}, {})",
331 Sugg::hir(cx, receiver, "..").maybe_par(),
332 Sugg::hir(cx, receiver, ".."),
333 Sugg::hir(cx, other_addend, ".."),
335 Applicability::MachineApplicable,
343 fn detect_hypot(cx: &LateContext<'_>, receiver: &Expr<'_>) -> Option<String> {
344 if let ExprKind::Binary(
346 node: BinOpKind::Add, ..
352 // check if expression of the form x * x + y * y
354 if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, lmul_lhs, lmul_rhs) = add_lhs.kind;
355 if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, rmul_lhs, rmul_rhs) = add_rhs.kind;
356 if eq_expr_value(cx, lmul_lhs, lmul_rhs);
357 if eq_expr_value(cx, rmul_lhs, rmul_rhs);
359 return Some(format!("{}.hypot({})", Sugg::hir(cx, lmul_lhs, "..").maybe_par(), Sugg::hir(cx, rmul_lhs, "..")));
363 // check if expression of the form x.powi(2) + y.powi(2)
365 if let ExprKind::MethodCall(
366 PathSegment { ident: lmethod_name, .. },
367 largs_0, [largs_1, ..],
370 if let ExprKind::MethodCall(
371 PathSegment { ident: rmethod_name, .. },
372 rargs_0, [rargs_1, ..],
375 if lmethod_name.as_str() == "powi" && rmethod_name.as_str() == "powi";
376 if let Some((lvalue, _)) = constant(cx, cx.typeck_results(), largs_1);
377 if let Some((rvalue, _)) = constant(cx, cx.typeck_results(), rargs_1);
378 if Int(2) == lvalue && Int(2) == rvalue;
380 return Some(format!("{}.hypot({})", Sugg::hir(cx, largs_0, "..").maybe_par(), Sugg::hir(cx, rargs_0, "..")));
388 fn check_hypot(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>) {
389 if let Some(message) = detect_hypot(cx, receiver) {
394 "hypotenuse can be computed more accurately",
397 Applicability::MachineApplicable,
402 // TODO: Lint expressions of the form `x.exp() - y` where y > 1
403 // and suggest usage of `x.exp_m1() - (y - 1)` instead
404 fn check_expm1(cx: &LateContext<'_>, expr: &Expr<'_>) {
406 if let ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, lhs, rhs) = expr.kind;
407 if cx.typeck_results().expr_ty(lhs).is_floating_point();
408 if let Some((value, _)) = constant(cx, cx.typeck_results(), rhs);
409 if F32(1.0) == value || F64(1.0) == value;
410 if let ExprKind::MethodCall(path, self_arg, ..) = &lhs.kind;
411 if cx.typeck_results().expr_ty(self_arg).is_floating_point();
412 if path.ident.name.as_str() == "exp";
418 "(e.pow(x) - 1) can be computed more accurately",
422 Sugg::hir(cx, self_arg, "..").maybe_par()
424 Applicability::MachineApplicable,
430 fn is_float_mul_expr<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<(&'a Expr<'a>, &'a Expr<'a>)> {
432 if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, lhs, rhs) = &expr.kind;
433 if cx.typeck_results().expr_ty(lhs).is_floating_point();
434 if cx.typeck_results().expr_ty(rhs).is_floating_point();
436 return Some((lhs, rhs));
443 // TODO: Fix rust-lang/rust-clippy#4735
444 fn check_mul_add(cx: &LateContext<'_>, expr: &Expr<'_>) {
445 if let ExprKind::Binary(
447 node: BinOpKind::Add, ..
453 if let Some(parent) = get_parent_expr(cx, expr) {
454 if let ExprKind::MethodCall(PathSegment { ident: method_name, .. }, receiver, ..) = parent.kind {
455 if method_name.as_str() == "sqrt" && detect_hypot(cx, receiver).is_some() {
461 let (recv, arg1, arg2) = if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, lhs) {
462 (inner_lhs, inner_rhs, rhs)
463 } else if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, rhs) {
464 (inner_lhs, inner_rhs, lhs)
473 "multiply and add expressions can be calculated more efficiently and accurately",
476 "{}.mul_add({}, {})",
477 prepare_receiver_sugg(cx, recv),
478 Sugg::hir(cx, arg1, ".."),
479 Sugg::hir(cx, arg2, ".."),
481 Applicability::MachineApplicable,
486 /// Returns true iff expr is an expression which tests whether or not
487 /// test is positive or an expression which tests whether or not test
489 /// Used for check-custom-abs function below
490 fn is_testing_positive(cx: &LateContext<'_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
491 if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
493 BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, right) && eq_expr_value(cx, left, test),
494 BinOpKind::Lt | BinOpKind::Le => is_zero(cx, left) && eq_expr_value(cx, right, test),
502 /// See [`is_testing_positive`]
503 fn is_testing_negative(cx: &LateContext<'_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
504 if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
506 BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, left) && eq_expr_value(cx, right, test),
507 BinOpKind::Lt | BinOpKind::Le => is_zero(cx, right) && eq_expr_value(cx, left, test),
515 /// Returns true iff expr is some zero literal
516 fn is_zero(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
517 match constant_simple(cx, cx.typeck_results(), expr) {
518 Some(Constant::Int(i)) => i == 0,
519 Some(Constant::F32(f)) => f == 0.0,
520 Some(Constant::F64(f)) => f == 0.0,
525 /// If the two expressions are negations of each other, then it returns
526 /// a tuple, in which the first element is true iff expr1 is the
527 /// positive expressions, and the second element is the positive
528 /// one of the two expressions
529 /// If the two expressions are not negations of each other, then it
531 fn are_negated<'a>(cx: &LateContext<'_>, expr1: &'a Expr<'a>, expr2: &'a Expr<'a>) -> Option<(bool, &'a Expr<'a>)> {
532 if let ExprKind::Unary(UnOp::Neg, expr1_negated) = &expr1.kind {
533 if eq_expr_value(cx, expr1_negated, expr2) {
534 return Some((false, expr2));
537 if let ExprKind::Unary(UnOp::Neg, expr2_negated) = &expr2.kind {
538 if eq_expr_value(cx, expr1, expr2_negated) {
539 return Some((true, expr1));
545 fn check_custom_abs(cx: &LateContext<'_>, expr: &Expr<'_>) {
547 if let Some(higher::If { cond, then, r#else: Some(r#else) }) = higher::If::hir(expr);
548 let if_body_expr = peel_blocks(then);
549 let else_body_expr = peel_blocks(r#else);
550 if let Some((if_expr_positive, body)) = are_negated(cx, if_body_expr, else_body_expr);
552 let positive_abs_sugg = (
553 "manual implementation of `abs` method",
554 format!("{}.abs()", Sugg::hir(cx, body, "..").maybe_par()),
556 let negative_abs_sugg = (
557 "manual implementation of negation of `abs` method",
558 format!("-{}.abs()", Sugg::hir(cx, body, "..").maybe_par()),
560 let sugg = if is_testing_positive(cx, cond, body) {
561 if if_expr_positive {
566 } else if is_testing_negative(cx, cond, body) {
567 if if_expr_positive {
582 Applicability::MachineApplicable,
588 fn are_same_base_logs(cx: &LateContext<'_>, expr_a: &Expr<'_>, expr_b: &Expr<'_>) -> bool {
590 if let ExprKind::MethodCall(PathSegment { ident: method_name_a, .. }, _, args_a, _) = expr_a.kind;
591 if let ExprKind::MethodCall(PathSegment { ident: method_name_b, .. }, _, args_b, _) = expr_b.kind;
593 return method_name_a.as_str() == method_name_b.as_str() &&
594 args_a.len() == args_b.len() &&
596 ["ln", "log2", "log10"].contains(&method_name_a.as_str()) ||
597 method_name_a.as_str() == "log" && args_a.len() == 1 && eq_expr_value(cx, &args_a[0], &args_b[0])
605 fn check_log_division(cx: &LateContext<'_>, expr: &Expr<'_>) {
606 // check if expression of the form x.logN() / y.logN()
608 if let ExprKind::Binary(
610 node: BinOpKind::Div, ..
615 if are_same_base_logs(cx, lhs, rhs);
616 if let ExprKind::MethodCall(_, largs_self, ..) = &lhs.kind;
617 if let ExprKind::MethodCall(_, rargs_self, ..) = &rhs.kind;
623 "log base can be expressed more clearly",
625 format!("{}.log({})", Sugg::hir(cx, largs_self, "..").maybe_par(), Sugg::hir(cx, rargs_self, ".."),),
626 Applicability::MachineApplicable,
632 fn check_radians(cx: &LateContext<'_>, expr: &Expr<'_>) {
634 if let ExprKind::Binary(
636 node: BinOpKind::Div, ..
641 if let ExprKind::Binary(
643 node: BinOpKind::Mul, ..
648 if let Some((rvalue, _)) = constant(cx, cx.typeck_results(), div_rhs);
649 if let Some((lvalue, _)) = constant(cx, cx.typeck_results(), mul_rhs);
651 // TODO: also check for constant values near PI/180 or 180/PI
652 if (F32(f32_consts::PI) == rvalue || F64(f64_consts::PI) == rvalue) &&
653 (F32(180_f32) == lvalue || F64(180_f64) == lvalue)
655 let mut proposal = format!("{}.to_degrees()", Sugg::hir(cx, mul_lhs, "..").maybe_par());
657 if let ExprKind::Lit(ref literal) = mul_lhs.kind;
658 if let ast::LitKind::Float(ref value, float_type) = literal.node;
659 if float_type == ast::LitFloatType::Unsuffixed;
661 if value.as_str().ends_with('.') {
662 proposal = format!("{}0_f64.to_degrees()", Sugg::hir(cx, mul_lhs, ".."));
664 proposal = format!("{}_f64.to_degrees()", Sugg::hir(cx, mul_lhs, ".."));
672 "conversion to degrees can be done more accurately",
675 Applicability::MachineApplicable,
678 (F32(180_f32) == rvalue || F64(180_f64) == rvalue) &&
679 (F32(f32_consts::PI) == lvalue || F64(f64_consts::PI) == lvalue)
681 let mut proposal = format!("{}.to_radians()", Sugg::hir(cx, mul_lhs, "..").maybe_par());
683 if let ExprKind::Lit(ref literal) = mul_lhs.kind;
684 if let ast::LitKind::Float(ref value, float_type) = literal.node;
685 if float_type == ast::LitFloatType::Unsuffixed;
687 if value.as_str().ends_with('.') {
688 proposal = format!("{}0_f64.to_radians()", Sugg::hir(cx, mul_lhs, ".."));
690 proposal = format!("{}_f64.to_radians()", Sugg::hir(cx, mul_lhs, ".."));
698 "conversion to radians can be done more accurately",
701 Applicability::MachineApplicable,
708 impl<'tcx> LateLintPass<'tcx> for FloatingPointArithmetic {
709 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
710 // All of these operations are currently not const.
711 if in_constant(cx, expr.hir_id) {
715 if let ExprKind::MethodCall(path, receiver, args, _) = &expr.kind {
716 let recv_ty = cx.typeck_results().expr_ty(receiver);
718 if recv_ty.is_floating_point() {
719 match path.ident.name.as_str() {
720 "ln" => check_ln1p(cx, expr, receiver),
721 "log" => check_log_base(cx, expr, receiver, args),
722 "powf" => check_powf(cx, expr, receiver, args),
723 "powi" => check_powi(cx, expr, receiver, args),
724 "sqrt" => check_hypot(cx, expr, receiver),
729 check_expm1(cx, expr);
730 check_mul_add(cx, expr);
731 check_custom_abs(cx, expr);
732 check_log_division(cx, expr);
733 check_radians(cx, expr);