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;
146 // Check for float literals without numbers following the decimal
147 // separator such as `2.` and adds a trailing zero
148 if sym.as_str().ends_with('.') {
156 suggestion = match suggestion {
157 Sugg::MaybeParen(_) => Sugg::MaybeParen(op),
158 _ => Sugg::NonParen(op)
163 suggestion.maybe_par()
166 fn check_log_base(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args: &[Expr<'_>]) {
167 if let Some(method) = get_specialized_log_method(cx, &args[0]) {
172 "logarithm for bases 2, 10 and e can be computed more accurately",
174 format!("{}.{method}()", Sugg::hir(cx, receiver, "..").maybe_par()),
175 Applicability::MachineApplicable,
180 // TODO: Lint expressions of the form `(x + y).ln()` where y > 1 and
181 // suggest usage of `(x + (y - 1)).ln_1p()` instead
182 fn check_ln1p(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>) {
183 if let ExprKind::Binary(
185 node: BinOpKind::Add, ..
192 constant(cx, cx.typeck_results(), lhs),
193 constant(cx, cx.typeck_results(), rhs),
195 (Some((value, _)), _) if F32(1.0) == value || F64(1.0) == value => rhs,
196 (_, Some((value, _))) if F32(1.0) == value || F64(1.0) == value => lhs,
204 "ln(1 + x) can be computed more accurately",
206 format!("{}.ln_1p()", prepare_receiver_sugg(cx, recv)),
207 Applicability::MachineApplicable,
212 // Returns an integer if the float constant is a whole number and it can be
213 // converted to an integer without loss of precision. For now we only check
214 // ranges [-16777215, 16777216) for type f32 as whole number floats outside
215 // this range are lossy and ambiguous.
216 #[expect(clippy::cast_possible_truncation)]
217 fn get_integer_from_float_constant(value: &Constant) -> Option<i32> {
219 F32(num) if num.fract() == 0.0 => {
220 if (-16_777_215.0..16_777_216.0).contains(num) {
221 Some(num.round() as i32)
226 F64(num) if num.fract() == 0.0 => {
227 if (-2_147_483_648.0..2_147_483_648.0).contains(num) {
228 Some(num.round() as i32)
237 fn check_powf(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args: &[Expr<'_>]) {
239 if let Some((value, _)) = constant(cx, cx.typeck_results(), receiver) {
240 if let Some(method) = if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
242 } else if F32(2.0) == value || F64(2.0) == value {
251 "exponent for bases 2 and e can be computed more accurately",
253 format!("{}.{method}()", prepare_receiver_sugg(cx, &args[0])),
254 Applicability::MachineApplicable,
260 if let Some((value, _)) = constant(cx, cx.typeck_results(), &args[0]) {
261 let (lint, help, suggestion) = if F32(1.0 / 2.0) == value || F64(1.0 / 2.0) == value {
264 "square-root of a number can be computed more efficiently and accurately",
265 format!("{}.sqrt()", Sugg::hir(cx, receiver, "..").maybe_par()),
267 } else if F32(1.0 / 3.0) == value || F64(1.0 / 3.0) == value {
270 "cube-root of a number can be computed more accurately",
271 format!("{}.cbrt()", Sugg::hir(cx, receiver, "..").maybe_par()),
273 } else if let Some(exponent) = get_integer_from_float_constant(&value) {
276 "exponentiation with integer powers can be computed more efficiently",
279 Sugg::hir(cx, receiver, "..").maybe_par(),
280 numeric_literal::format(&exponent.to_string(), None, false)
294 Applicability::MachineApplicable,
299 fn check_powi(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args: &[Expr<'_>]) {
300 if let Some((value, _)) = constant(cx, cx.typeck_results(), &args[0]) {
302 if let Some(parent) = get_parent_expr(cx, expr) {
303 if let Some(grandparent) = get_parent_expr(cx, parent) {
304 if let ExprKind::MethodCall(PathSegment { ident: method_name, .. }, receiver, ..) = grandparent.kind
306 if method_name.as_str() == "sqrt" && detect_hypot(cx, receiver).is_some() {
312 if let ExprKind::Binary(
314 node: op @ (BinOpKind::Add | BinOpKind::Sub),
321 let other_addend = if lhs.hir_id == expr.hir_id { rhs } else { lhs };
323 // Negate expr if original code has subtraction and expr is on the right side
324 let maybe_neg_sugg = |expr, hir_id| {
325 let sugg = Sugg::hir(cx, expr, "..");
326 if matches!(op, BinOpKind::Sub) && hir_id == rhs.hir_id {
337 "multiply and add expressions can be calculated more efficiently and accurately",
340 "{}.mul_add({}, {})",
341 Sugg::hir(cx, receiver, "..").maybe_par(),
342 maybe_neg_sugg(receiver, expr.hir_id),
343 maybe_neg_sugg(other_addend, other_addend.hir_id),
345 Applicability::MachineApplicable,
353 fn detect_hypot(cx: &LateContext<'_>, receiver: &Expr<'_>) -> Option<String> {
354 if let ExprKind::Binary(
356 node: BinOpKind::Add, ..
362 // check if expression of the form x * x + y * y
364 if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, lmul_lhs, lmul_rhs) = add_lhs.kind;
365 if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, rmul_lhs, rmul_rhs) = add_rhs.kind;
366 if eq_expr_value(cx, lmul_lhs, lmul_rhs);
367 if eq_expr_value(cx, rmul_lhs, rmul_rhs);
369 return Some(format!("{}.hypot({})", Sugg::hir(cx, lmul_lhs, "..").maybe_par(), Sugg::hir(cx, rmul_lhs, "..")));
373 // check if expression of the form x.powi(2) + y.powi(2)
375 if let ExprKind::MethodCall(
376 PathSegment { ident: lmethod_name, .. },
377 largs_0, [largs_1, ..],
380 if let ExprKind::MethodCall(
381 PathSegment { ident: rmethod_name, .. },
382 rargs_0, [rargs_1, ..],
385 if lmethod_name.as_str() == "powi" && rmethod_name.as_str() == "powi";
386 if let Some((lvalue, _)) = constant(cx, cx.typeck_results(), largs_1);
387 if let Some((rvalue, _)) = constant(cx, cx.typeck_results(), rargs_1);
388 if Int(2) == lvalue && Int(2) == rvalue;
390 return Some(format!("{}.hypot({})", Sugg::hir(cx, largs_0, "..").maybe_par(), Sugg::hir(cx, rargs_0, "..")));
398 fn check_hypot(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>) {
399 if let Some(message) = detect_hypot(cx, receiver) {
404 "hypotenuse can be computed more accurately",
407 Applicability::MachineApplicable,
412 // TODO: Lint expressions of the form `x.exp() - y` where y > 1
413 // and suggest usage of `x.exp_m1() - (y - 1)` instead
414 fn check_expm1(cx: &LateContext<'_>, expr: &Expr<'_>) {
416 if let ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, lhs, rhs) = expr.kind;
417 if cx.typeck_results().expr_ty(lhs).is_floating_point();
418 if let Some((value, _)) = constant(cx, cx.typeck_results(), rhs);
419 if F32(1.0) == value || F64(1.0) == value;
420 if let ExprKind::MethodCall(path, self_arg, ..) = &lhs.kind;
421 if cx.typeck_results().expr_ty(self_arg).is_floating_point();
422 if path.ident.name.as_str() == "exp";
428 "(e.pow(x) - 1) can be computed more accurately",
432 Sugg::hir(cx, self_arg, "..").maybe_par()
434 Applicability::MachineApplicable,
440 fn is_float_mul_expr<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<(&'a Expr<'a>, &'a Expr<'a>)> {
442 if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, lhs, rhs) = &expr.kind;
443 if cx.typeck_results().expr_ty(lhs).is_floating_point();
444 if cx.typeck_results().expr_ty(rhs).is_floating_point();
446 return Some((lhs, rhs));
453 // TODO: Fix rust-lang/rust-clippy#4735
454 fn check_mul_add(cx: &LateContext<'_>, expr: &Expr<'_>) {
455 if let ExprKind::Binary(
457 node: op @ (BinOpKind::Add | BinOpKind::Sub),
464 if let Some(parent) = get_parent_expr(cx, expr) {
465 if let ExprKind::MethodCall(PathSegment { ident: method_name, .. }, receiver, ..) = parent.kind {
466 if method_name.as_str() == "sqrt" && detect_hypot(cx, receiver).is_some() {
472 let maybe_neg_sugg = |expr| {
473 let sugg = Sugg::hir(cx, expr, "..");
474 if let BinOpKind::Sub = op {
481 let (recv, arg1, arg2) = if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, lhs) {
484 Sugg::hir(cx, inner_rhs, "..").to_string(),
487 } else if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, rhs) {
490 maybe_neg_sugg(inner_rhs),
491 Sugg::hir(cx, lhs, "..").to_string(),
501 "multiply and add expressions can be calculated more efficiently and accurately",
503 format!("{}.mul_add({arg1}, {arg2})", prepare_receiver_sugg(cx, recv)),
504 Applicability::MachineApplicable,
509 /// Returns true iff expr is an expression which tests whether or not
510 /// test is positive or an expression which tests whether or not test
512 /// Used for check-custom-abs function below
513 fn is_testing_positive(cx: &LateContext<'_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
514 if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
516 BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, right) && eq_expr_value(cx, left, test),
517 BinOpKind::Lt | BinOpKind::Le => is_zero(cx, left) && eq_expr_value(cx, right, test),
525 /// See [`is_testing_positive`]
526 fn is_testing_negative(cx: &LateContext<'_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
527 if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
529 BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, left) && eq_expr_value(cx, right, test),
530 BinOpKind::Lt | BinOpKind::Le => is_zero(cx, right) && eq_expr_value(cx, left, test),
538 /// Returns true iff expr is some zero literal
539 fn is_zero(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
540 match constant_simple(cx, cx.typeck_results(), expr) {
541 Some(Constant::Int(i)) => i == 0,
542 Some(Constant::F32(f)) => f == 0.0,
543 Some(Constant::F64(f)) => f == 0.0,
548 /// If the two expressions are negations of each other, then it returns
549 /// a tuple, in which the first element is true iff expr1 is the
550 /// positive expressions, and the second element is the positive
551 /// one of the two expressions
552 /// If the two expressions are not negations of each other, then it
554 fn are_negated<'a>(cx: &LateContext<'_>, expr1: &'a Expr<'a>, expr2: &'a Expr<'a>) -> Option<(bool, &'a Expr<'a>)> {
555 if let ExprKind::Unary(UnOp::Neg, expr1_negated) = &expr1.kind {
556 if eq_expr_value(cx, expr1_negated, expr2) {
557 return Some((false, expr2));
560 if let ExprKind::Unary(UnOp::Neg, expr2_negated) = &expr2.kind {
561 if eq_expr_value(cx, expr1, expr2_negated) {
562 return Some((true, expr1));
568 fn check_custom_abs(cx: &LateContext<'_>, expr: &Expr<'_>) {
570 if let Some(higher::If { cond, then, r#else: Some(r#else) }) = higher::If::hir(expr);
571 let if_body_expr = peel_blocks(then);
572 let else_body_expr = peel_blocks(r#else);
573 if let Some((if_expr_positive, body)) = are_negated(cx, if_body_expr, else_body_expr);
575 let positive_abs_sugg = (
576 "manual implementation of `abs` method",
577 format!("{}.abs()", Sugg::hir(cx, body, "..").maybe_par()),
579 let negative_abs_sugg = (
580 "manual implementation of negation of `abs` method",
581 format!("-{}.abs()", Sugg::hir(cx, body, "..").maybe_par()),
583 let sugg = if is_testing_positive(cx, cond, body) {
584 if if_expr_positive {
589 } else if is_testing_negative(cx, cond, body) {
590 if if_expr_positive {
605 Applicability::MachineApplicable,
611 fn are_same_base_logs(cx: &LateContext<'_>, expr_a: &Expr<'_>, expr_b: &Expr<'_>) -> bool {
613 if let ExprKind::MethodCall(PathSegment { ident: method_name_a, .. }, _, args_a, _) = expr_a.kind;
614 if let ExprKind::MethodCall(PathSegment { ident: method_name_b, .. }, _, args_b, _) = expr_b.kind;
616 return method_name_a.as_str() == method_name_b.as_str() &&
617 args_a.len() == args_b.len() &&
619 ["ln", "log2", "log10"].contains(&method_name_a.as_str()) ||
620 method_name_a.as_str() == "log" && args_a.len() == 1 && eq_expr_value(cx, &args_a[0], &args_b[0])
628 fn check_log_division(cx: &LateContext<'_>, expr: &Expr<'_>) {
629 // check if expression of the form x.logN() / y.logN()
631 if let ExprKind::Binary(
633 node: BinOpKind::Div, ..
638 if are_same_base_logs(cx, lhs, rhs);
639 if let ExprKind::MethodCall(_, largs_self, ..) = &lhs.kind;
640 if let ExprKind::MethodCall(_, rargs_self, ..) = &rhs.kind;
646 "log base can be expressed more clearly",
648 format!("{}.log({})", Sugg::hir(cx, largs_self, "..").maybe_par(), Sugg::hir(cx, rargs_self, ".."),),
649 Applicability::MachineApplicable,
655 fn check_radians(cx: &LateContext<'_>, expr: &Expr<'_>) {
657 if let ExprKind::Binary(
659 node: BinOpKind::Div, ..
664 if let ExprKind::Binary(
666 node: BinOpKind::Mul, ..
671 if let Some((rvalue, _)) = constant(cx, cx.typeck_results(), div_rhs);
672 if let Some((lvalue, _)) = constant(cx, cx.typeck_results(), mul_rhs);
674 // TODO: also check for constant values near PI/180 or 180/PI
675 if (F32(f32_consts::PI) == rvalue || F64(f64_consts::PI) == rvalue) &&
676 (F32(180_f32) == lvalue || F64(180_f64) == lvalue)
678 let mut proposal = format!("{}.to_degrees()", Sugg::hir(cx, mul_lhs, "..").maybe_par());
680 if let ExprKind::Lit(ref literal) = mul_lhs.kind;
681 if let ast::LitKind::Float(ref value, float_type) = literal.node;
682 if float_type == ast::LitFloatType::Unsuffixed;
684 if value.as_str().ends_with('.') {
685 proposal = format!("{}0_f64.to_degrees()", Sugg::hir(cx, mul_lhs, ".."));
687 proposal = format!("{}_f64.to_degrees()", Sugg::hir(cx, mul_lhs, ".."));
695 "conversion to degrees can be done more accurately",
698 Applicability::MachineApplicable,
701 (F32(180_f32) == rvalue || F64(180_f64) == rvalue) &&
702 (F32(f32_consts::PI) == lvalue || F64(f64_consts::PI) == lvalue)
704 let mut proposal = format!("{}.to_radians()", Sugg::hir(cx, mul_lhs, "..").maybe_par());
706 if let ExprKind::Lit(ref literal) = mul_lhs.kind;
707 if let ast::LitKind::Float(ref value, float_type) = literal.node;
708 if float_type == ast::LitFloatType::Unsuffixed;
710 if value.as_str().ends_with('.') {
711 proposal = format!("{}0_f64.to_radians()", Sugg::hir(cx, mul_lhs, ".."));
713 proposal = format!("{}_f64.to_radians()", Sugg::hir(cx, mul_lhs, ".."));
721 "conversion to radians can be done more accurately",
724 Applicability::MachineApplicable,
731 impl<'tcx> LateLintPass<'tcx> for FloatingPointArithmetic {
732 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
733 // All of these operations are currently not const.
734 if in_constant(cx, expr.hir_id) {
738 if let ExprKind::MethodCall(path, receiver, args, _) = &expr.kind {
739 let recv_ty = cx.typeck_results().expr_ty(receiver);
741 if recv_ty.is_floating_point() {
742 match path.ident.name.as_str() {
743 "ln" => check_ln1p(cx, expr, receiver),
744 "log" => check_log_base(cx, expr, receiver, args),
745 "powf" => check_powf(cx, expr, receiver, args),
746 "powi" => check_powi(cx, expr, receiver, args),
747 "sqrt" => check_hypot(cx, expr, receiver),
752 check_expm1(cx, expr);
753 check_mul_add(cx, expr);
754 check_custom_abs(cx, expr);
755 check_log_division(cx, expr);
756 check_radians(cx, expr);