2 constant, constant_simple, Constant,
3 Constant::{Int, F32, F64},
5 use clippy_utils::diagnostics::span_lint_and_sugg;
6 use clippy_utils::{eq_expr_value, get_parent_expr, numeric_literal, sugg};
7 use if_chain::if_chain;
8 use rustc_errors::Applicability;
9 use rustc_hir::{BinOpKind, Expr, ExprKind, PathSegment, UnOp};
10 use rustc_lint::{LateContext, LateLintPass};
12 use rustc_session::{declare_lint_pass, declare_tool_lint};
13 use rustc_span::source_map::Spanned;
16 use std::f32::consts as f32_consts;
17 use std::f64::consts as f64_consts;
20 declare_clippy_lint! {
21 /// **What it does:** Looks for floating-point expressions that
22 /// can be expressed using built-in methods to improve accuracy
23 /// at the cost of performance.
25 /// **Why is this bad?** Negatively impacts accuracy.
27 /// **Known problems:** None
33 /// let _ = a.powf(1.0 / 3.0);
34 /// let _ = (1.0 + a).ln();
35 /// let _ = a.exp() - 1.0;
38 /// is better expressed as
43 /// let _ = a.ln_1p();
44 /// let _ = a.exp_m1();
48 "usage of imprecise floating point operations"
51 declare_clippy_lint! {
52 /// **What it does:** Looks for floating-point expressions that
53 /// can be expressed using built-in methods to improve both
54 /// accuracy and performance.
56 /// **Why is this bad?** Negatively impacts accuracy and performance.
58 /// **Known problems:** None
63 /// use std::f32::consts::E;
66 /// let _ = (2f32).powf(a);
67 /// let _ = E.powf(a);
68 /// let _ = a.powf(1.0 / 2.0);
69 /// let _ = a.log(2.0);
70 /// let _ = a.log(10.0);
72 /// let _ = a.powf(2.0);
73 /// let _ = a * 2.0 + 4.0;
74 /// let _ = if a < 0.0 {
79 /// let _ = if a < 0.0 {
86 /// is better expressed as
89 /// use std::f32::consts::E;
96 /// let _ = a.log10();
98 /// let _ = a.powi(2);
99 /// let _ = a.mul_add(2.0, 4.0);
101 /// let _ = -a.abs();
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<'_>, args: &[Expr<'_>]) {
168 if let Some(method) = get_specialized_log_method(cx, &args[1]) {
173 "logarithm for bases 2, 10 and e can be computed more accurately",
175 format!("{}.{}()", Sugg::hir(cx, &args[0], ".."), 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<'_>, args: &[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 #[allow(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<'_>, args: &[Expr<'_>]) {
240 if let Some((value, _)) = constant(cx, cx.typeck_results(), &args[0]) {
241 let method = if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
243 } else if F32(2.0) == value || F64(2.0) == value {
253 "exponent for bases 2 and e can be computed more accurately",
255 format!("{}.{}()", prepare_receiver_sugg(cx, &args[1]), method),
256 Applicability::MachineApplicable,
261 if let Some((value, _)) = constant(cx, cx.typeck_results(), &args[1]) {
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, &args[0], "..")),
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, &args[0], "..")),
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, &args[0], ".."),
281 numeric_literal::format(&exponent.to_string(), None, false)
295 Applicability::MachineApplicable,
300 fn check_powi(cx: &LateContext<'_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
301 if let Some((value, _)) = constant(cx, cx.typeck_results(), &args[1]) {
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, .. }, _, args, _) = grandparent.kind {
306 if method_name.as_str() == "sqrt" && detect_hypot(cx, args).is_some() {
312 if let ExprKind::Binary(
314 node: BinOpKind::Add, ..
320 let other_addend = if lhs.hir_id == expr.hir_id { rhs } else { lhs };
326 "multiply and add expressions can be calculated more efficiently and accurately",
329 "{}.mul_add({}, {})",
330 Sugg::hir(cx, &args[0], ".."),
331 Sugg::hir(cx, &args[0], ".."),
332 Sugg::hir(cx, other_addend, ".."),
334 Applicability::MachineApplicable,
344 fn detect_hypot(cx: &LateContext<'_>, args: &[Expr<'_>]) -> Option<String> {
345 if let ExprKind::Binary(
347 node: BinOpKind::Add, ..
353 // check if expression of the form x * x + y * y
355 if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, lmul_lhs, lmul_rhs) = add_lhs.kind;
356 if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, rmul_lhs, rmul_rhs) = add_rhs.kind;
357 if eq_expr_value(cx, lmul_lhs, lmul_rhs);
358 if eq_expr_value(cx, rmul_lhs, rmul_rhs);
360 return Some(format!("{}.hypot({})", Sugg::hir(cx, lmul_lhs, ".."), Sugg::hir(cx, rmul_lhs, "..")));
364 // check if expression of the form x.powi(2) + y.powi(2)
366 if let ExprKind::MethodCall(
367 PathSegment { ident: lmethod_name, .. },
372 if let ExprKind::MethodCall(
373 PathSegment { ident: rmethod_name, .. },
378 if lmethod_name.as_str() == "powi" && rmethod_name.as_str() == "powi";
379 if let Some((lvalue, _)) = constant(cx, cx.typeck_results(), &largs[1]);
380 if let Some((rvalue, _)) = constant(cx, cx.typeck_results(), &rargs[1]);
381 if Int(2) == lvalue && Int(2) == rvalue;
383 return Some(format!("{}.hypot({})", Sugg::hir(cx, &largs[0], ".."), Sugg::hir(cx, &rargs[0], "..")));
391 fn check_hypot(cx: &LateContext<'_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
392 if let Some(message) = detect_hypot(cx, args) {
397 "hypotenuse can be computed more accurately",
400 Applicability::MachineApplicable,
405 // TODO: Lint expressions of the form `x.exp() - y` where y > 1
406 // and suggest usage of `x.exp_m1() - (y - 1)` instead
407 fn check_expm1(cx: &LateContext<'_>, expr: &Expr<'_>) {
409 if let ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, lhs, rhs) = expr.kind;
410 if cx.typeck_results().expr_ty(lhs).is_floating_point();
411 if let Some((value, _)) = constant(cx, cx.typeck_results(), rhs);
412 if F32(1.0) == value || F64(1.0) == value;
413 if let ExprKind::MethodCall(path, _, method_args, _) = lhs.kind;
414 if cx.typeck_results().expr_ty(&method_args[0]).is_floating_point();
415 if path.ident.name.as_str() == "exp";
421 "(e.pow(x) - 1) can be computed more accurately",
425 Sugg::hir(cx, &method_args[0], "..")
427 Applicability::MachineApplicable,
433 fn is_float_mul_expr<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<(&'a Expr<'a>, &'a Expr<'a>)> {
435 if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, lhs, rhs) = &expr.kind;
436 if cx.typeck_results().expr_ty(lhs).is_floating_point();
437 if cx.typeck_results().expr_ty(rhs).is_floating_point();
439 return Some((lhs, rhs));
446 // TODO: Fix rust-lang/rust-clippy#4735
447 fn check_mul_add(cx: &LateContext<'_>, expr: &Expr<'_>) {
448 if let ExprKind::Binary(
450 node: BinOpKind::Add, ..
456 if let Some(parent) = get_parent_expr(cx, expr) {
457 if let ExprKind::MethodCall(PathSegment { ident: method_name, .. }, _, args, _) = parent.kind {
458 if method_name.as_str() == "sqrt" && detect_hypot(cx, args).is_some() {
464 let (recv, arg1, arg2) = if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, lhs) {
465 (inner_lhs, inner_rhs, rhs)
466 } else if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, rhs) {
467 (inner_lhs, inner_rhs, lhs)
476 "multiply and add expressions can be calculated more efficiently and accurately",
479 "{}.mul_add({}, {})",
480 prepare_receiver_sugg(cx, recv),
481 Sugg::hir(cx, arg1, ".."),
482 Sugg::hir(cx, arg2, ".."),
484 Applicability::MachineApplicable,
489 /// Returns true iff expr is an expression which tests whether or not
490 /// test is positive or an expression which tests whether or not test
492 /// Used for check-custom-abs function below
493 fn is_testing_positive(cx: &LateContext<'_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
494 if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
496 BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, right) && eq_expr_value(cx, left, test),
497 BinOpKind::Lt | BinOpKind::Le => is_zero(cx, left) && eq_expr_value(cx, right, test),
505 /// See [`is_testing_positive`]
506 fn is_testing_negative(cx: &LateContext<'_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
507 if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
509 BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, left) && eq_expr_value(cx, right, test),
510 BinOpKind::Lt | BinOpKind::Le => is_zero(cx, right) && eq_expr_value(cx, left, test),
518 /// Returns true iff expr is some zero literal
519 fn is_zero(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
520 match constant_simple(cx, cx.typeck_results(), expr) {
521 Some(Constant::Int(i)) => i == 0,
522 Some(Constant::F32(f)) => f == 0.0,
523 Some(Constant::F64(f)) => f == 0.0,
528 /// If the two expressions are negations of each other, then it returns
529 /// a tuple, in which the first element is true iff expr1 is the
530 /// positive expressions, and the second element is the positive
531 /// one of the two expressions
532 /// If the two expressions are not negations of each other, then it
534 fn are_negated<'a>(cx: &LateContext<'_>, expr1: &'a Expr<'a>, expr2: &'a Expr<'a>) -> Option<(bool, &'a Expr<'a>)> {
535 if let ExprKind::Unary(UnOp::Neg, expr1_negated) = &expr1.kind {
536 if eq_expr_value(cx, expr1_negated, expr2) {
537 return Some((false, expr2));
540 if let ExprKind::Unary(UnOp::Neg, expr2_negated) = &expr2.kind {
541 if eq_expr_value(cx, expr1, expr2_negated) {
542 return Some((true, expr1));
548 fn check_custom_abs(cx: &LateContext<'_>, expr: &Expr<'_>) {
550 if let ExprKind::If(cond, body, else_body) = expr.kind;
551 if let ExprKind::Block(block, _) = body.kind;
552 if block.stmts.is_empty();
553 if let Some(if_body_expr) = block.expr;
554 if let Some(ExprKind::Block(else_block, _)) = else_body.map(|el| &el.kind);
555 if else_block.stmts.is_empty();
556 if let Some(else_body_expr) = else_block.expr;
557 if let Some((if_expr_positive, body)) = are_negated(cx, if_body_expr, else_body_expr);
559 let positive_abs_sugg = (
560 "manual implementation of `abs` method",
561 format!("{}.abs()", Sugg::hir(cx, body, "..")),
563 let negative_abs_sugg = (
564 "manual implementation of negation of `abs` method",
565 format!("-{}.abs()", Sugg::hir(cx, body, "..")),
567 let sugg = if is_testing_positive(cx, cond, body) {
568 if if_expr_positive {
573 } else if is_testing_negative(cx, cond, body) {
574 if if_expr_positive {
589 Applicability::MachineApplicable,
595 fn are_same_base_logs(cx: &LateContext<'_>, expr_a: &Expr<'_>, expr_b: &Expr<'_>) -> bool {
597 if let ExprKind::MethodCall(PathSegment { ident: method_name_a, .. }, _, args_a, _) = expr_a.kind;
598 if let ExprKind::MethodCall(PathSegment { ident: method_name_b, .. }, _, args_b, _) = expr_b.kind;
600 return method_name_a.as_str() == method_name_b.as_str() &&
601 args_a.len() == args_b.len() &&
603 ["ln", "log2", "log10"].contains(&&*method_name_a.as_str()) ||
604 method_name_a.as_str() == "log" && args_a.len() == 2 && eq_expr_value(cx, &args_a[1], &args_b[1])
612 fn check_log_division(cx: &LateContext<'_>, expr: &Expr<'_>) {
613 // check if expression of the form x.logN() / y.logN()
615 if let ExprKind::Binary(
617 node: BinOpKind::Div, ..
622 if are_same_base_logs(cx, lhs, rhs);
623 if let ExprKind::MethodCall(_, _, largs, _) = lhs.kind;
624 if let ExprKind::MethodCall(_, _, rargs, _) = rhs.kind;
630 "log base can be expressed more clearly",
632 format!("{}.log({})", Sugg::hir(cx, &largs[0], ".."), Sugg::hir(cx, &rargs[0], ".."),),
633 Applicability::MachineApplicable,
639 fn check_radians(cx: &LateContext<'_>, expr: &Expr<'_>) {
641 if let ExprKind::Binary(
643 node: BinOpKind::Div, ..
648 if let ExprKind::Binary(
650 node: BinOpKind::Mul, ..
655 if let Some((rvalue, _)) = constant(cx, cx.typeck_results(), div_rhs);
656 if let Some((lvalue, _)) = constant(cx, cx.typeck_results(), mul_rhs);
658 // TODO: also check for constant values near PI/180 or 180/PI
659 if (F32(f32_consts::PI) == rvalue || F64(f64_consts::PI) == rvalue) &&
660 (F32(180_f32) == lvalue || F64(180_f64) == lvalue)
666 "conversion to degrees can be done more accurately",
668 format!("{}.to_degrees()", Sugg::hir(cx, mul_lhs, "..")),
669 Applicability::MachineApplicable,
672 (F32(180_f32) == rvalue || F64(180_f64) == rvalue) &&
673 (F32(f32_consts::PI) == lvalue || F64(f64_consts::PI) == lvalue)
679 "conversion to radians can be done more accurately",
681 format!("{}.to_radians()", Sugg::hir(cx, mul_lhs, "..")),
682 Applicability::MachineApplicable,
689 impl<'tcx> LateLintPass<'tcx> for FloatingPointArithmetic {
690 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
691 if let ExprKind::MethodCall(path, _, args, _) = &expr.kind {
692 let recv_ty = cx.typeck_results().expr_ty(&args[0]);
694 if recv_ty.is_floating_point() {
695 match &*path.ident.name.as_str() {
696 "ln" => check_ln1p(cx, expr, args),
697 "log" => check_log_base(cx, expr, args),
698 "powf" => check_powf(cx, expr, args),
699 "powi" => check_powi(cx, expr, args),
700 "sqrt" => check_hypot(cx, expr, args),
705 check_expm1(cx, expr);
706 check_mul_add(cx, expr);
707 check_custom_abs(cx, expr);
708 check_log_division(cx, expr);
709 check_radians(cx, expr);