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Addresses Issue #4001
Fixed typo Fixes lint name and uses appropriate linting suggestion changed lint help message Added autofixable test Added Autofixable Test Removed Broken Autofixable File updated lints Generated Autofixable/Nonfixable Test Cases Changed Suggestion Applicability Fixed Lint List Count
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‎CHANGELOG.md

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@@ -1063,6 +1063,7 @@ Released 2018-09-13
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[`logic_bug`]: https://rust-lang.github.io/rust-clippy/master/index.html#logic_bug
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[`main_recursion`]: https://rust-lang.github.io/rust-clippy/master/index.html#main_recursion
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[`manual_memcpy`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_memcpy
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[`manual_mul_add`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_mul_add
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[`manual_saturating_arithmetic`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_saturating_arithmetic
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[`manual_swap`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_swap
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[`many_single_char_names`]: https://rust-lang.github.io/rust-clippy/master/index.html#many_single_char_names

‎clippy_lints/src/lib.rs

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@@ -224,6 +224,7 @@ pub mod misc_early;
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pub mod missing_const_for_fn;
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pub mod missing_doc;
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pub mod missing_inline;
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pub mod mul_add;
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pub mod multiple_crate_versions;
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pub mod mut_mut;
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pub mod mut_reference;
@@ -604,6 +605,7 @@ pub fn register_plugins(reg: &mut rustc_driver::plugin::Registry<'_>, conf: &Con
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reg.register_late_lint_pass(box inherent_to_string::InherentToString);
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reg.register_late_lint_pass(box trait_bounds::TraitBounds);
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reg.register_late_lint_pass(box comparison_chain::ComparisonChain);
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reg.register_late_lint_pass(box mul_add::MulAddCheck);
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reg.register_lint_group("clippy::restriction", Some("clippy_restriction"), vec![
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arithmetic::FLOAT_ARITHMETIC,
@@ -836,6 +838,7 @@ pub fn register_plugins(reg: &mut rustc_driver::plugin::Registry<'_>, conf: &Con
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misc_early::UNNEEDED_FIELD_PATTERN,
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misc_early::UNNEEDED_WILDCARD_PATTERN,
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misc_early::ZERO_PREFIXED_LITERAL,
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mul_add::MANUAL_MUL_ADD,
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mut_reference::UNNECESSARY_MUT_PASSED,
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mutex_atomic::MUTEX_ATOMIC,
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needless_bool::BOOL_COMPARISON,
@@ -1173,6 +1176,7 @@ pub fn register_plugins(reg: &mut rustc_driver::plugin::Registry<'_>, conf: &Con
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methods::OR_FUN_CALL,
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methods::SINGLE_CHAR_PATTERN,
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misc::CMP_OWNED,
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mul_add::MANUAL_MUL_ADD,
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mutex_atomic::MUTEX_ATOMIC,
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redundant_clone::REDUNDANT_CLONE,
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slow_vector_initialization::SLOW_VECTOR_INITIALIZATION,

‎clippy_lints/src/mul_add.rs

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use rustc::hir::*;
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use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use rustc::{declare_lint_pass, declare_tool_lint};
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use rustc_errors::Applicability;
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use crate::utils::*;
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declare_clippy_lint! {
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/// **What it does:** Checks for expressions of the form `a * b + c`
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/// or `c + a * b` where `a`, `b`, `c` are floats and suggests using
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/// `a.mul_add(b, c)` instead.
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///
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/// **Why is this bad?** Calculating `a * b + c` may lead to slight
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/// numerical inaccuracies as `a * b` is rounded before being added to
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/// `c`. Depending on the target architecture, `mul_add()` may be more
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/// performant.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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///
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/// ```rust
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/// # let a = 0_f32;
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/// # let b = 0_f32;
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/// # let c = 0_f32;
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/// let foo = (a * b) + c;
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/// ```
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///
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/// can be written as
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///
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/// ```rust
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/// # let a = 0_f32;
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/// # let b = 0_f32;
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/// # let c = 0_f32;
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/// let foo = a.mul_add(b, c);
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/// ```
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pub MANUAL_MUL_ADD,
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perf,
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"Using `a.mul_add(b, c)` for floating points has higher numerical precision than `a * b + c`"
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}
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declare_lint_pass!(MulAddCheck => [MANUAL_MUL_ADD]);
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fn is_float<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr) -> bool {
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cx.tables.expr_ty(expr).is_floating_point()
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}
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// Checks whether expression is multiplication of two floats
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fn is_float_mult_expr<'a, 'tcx, 'b>(cx: &LateContext<'a, 'tcx>, expr: &'b Expr) -> Option<(&'b Expr, &'b Expr)> {
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if let ExprKind::Binary(op, lhs, rhs) = &expr.kind {
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if let BinOpKind::Mul = op.node {
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if is_float(cx, &lhs) && is_float(cx, &rhs) {
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return Some((&lhs, &rhs));
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}
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}
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}
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None
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MulAddCheck {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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if let ExprKind::Binary(op, lhs, rhs) = &expr.kind {
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if let BinOpKind::Add = op.node {
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//Converts mult_lhs * mult_rhs + rhs to mult_lhs.mult_add(mult_rhs, rhs)
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if let Some((mult_lhs, mult_rhs)) = is_float_mult_expr(cx, lhs) {
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if is_float(cx, rhs) {
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span_lint_and_sugg(
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cx,
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MANUAL_MUL_ADD,
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expr.span,
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"consider using mul_add() for better numerical precision",
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"try",
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format!(
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"{}.mul_add({}, {})",
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snippet(cx, mult_lhs.span, "_"),
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snippet(cx, mult_rhs.span, "_"),
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snippet(cx, rhs.span, "_"),
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),
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Applicability::MaybeIncorrect,
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);
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}
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}
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//Converts lhs + mult_lhs * mult_rhs to mult_lhs.mult_add(mult_rhs, lhs)
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if let Some((mult_lhs, mult_rhs)) = is_float_mult_expr(cx, rhs) {
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if is_float(cx, lhs) {
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span_lint_and_sugg(
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cx,
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MANUAL_MUL_ADD,
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expr.span,
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"consider using mul_add() for better numerical precision",
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"try",
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format!(
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"{}.mul_add({}, {})",
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snippet(cx, mult_lhs.span, "_"),
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snippet(cx, mult_rhs.span, "_"),
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snippet(cx, lhs.span, "_"),
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),
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Applicability::MaybeIncorrect,
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);
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}
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}
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}
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}
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}
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}

‎src/lintlist/mod.rs

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@@ -6,7 +6,7 @@ pub use lint::Lint;
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pub use lint::LINT_LEVELS;
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// begin lint list, do not remove this comment, it’s used in `update_lints`
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pub const ALL_LINTS: [Lint; 319] = [
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pub const ALL_LINTS: [Lint; 320] = [
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Lint {
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name: "absurd_extreme_comparisons",
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group: "correctness",
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deprecation: None,
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module: "loops",
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},
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Lint {
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name: "manual_mul_add",
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group: "perf",
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desc: "Using `a.mul_add(b, c)` for floating points has higher numerical precision than `a * b + c`",
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deprecation: None,
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module: "mul_add",
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},
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Lint {
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name: "manual_saturating_arithmetic",
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group: "style",

‎tests/ui/mul_add.rs

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#![warn(clippy::manual_mul_add)]
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#![allow(unused_variables)]
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fn mul_add_test() {
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let a: f64 = 1234.567;
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let b: f64 = 45.67834;
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let c: f64 = 0.0004;
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// Examples of not auto-fixable expressions
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let test1 = (a * b + c) * (c + a * b) + (c + (a * b) + c);
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let test2 = 1234.567 * 45.67834 + 0.0004;
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}
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fn main() {
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mul_add_test();
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}

‎tests/ui/mul_add.stderr

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error: consider using mul_add() for better numerical precision
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--> $DIR/mul_add.rs:10:17
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|
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LL | let test1 = (a * b + c) * (c + a * b) + (c + (a * b) + c);
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `(a * b + c).mul_add((c + a * b), (c + (a * b) + c))`
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|
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= note: `-D clippy::manual-mul-add` implied by `-D warnings`
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error: consider using mul_add() for better numerical precision
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--> $DIR/mul_add.rs:10:17
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|
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LL | let test1 = (a * b + c) * (c + a * b) + (c + (a * b) + c);
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| ^^^^^^^^^^^ help: try: `a.mul_add(b, c)`
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error: consider using mul_add() for better numerical precision
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--> $DIR/mul_add.rs:10:31
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|
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LL | let test1 = (a * b + c) * (c + a * b) + (c + (a * b) + c);
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| ^^^^^^^^^^^ help: try: `a.mul_add(b, c)`
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error: consider using mul_add() for better numerical precision
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--> $DIR/mul_add.rs:10:46
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|
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LL | let test1 = (a * b + c) * (c + a * b) + (c + (a * b) + c);
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| ^^^^^^^^^^^ help: try: `a.mul_add(b, c)`
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error: consider using mul_add() for better numerical precision
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--> $DIR/mul_add.rs:11:17
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|
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LL | let test2 = 1234.567 * 45.67834 + 0.0004;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `1234.567.mul_add(45.67834, 0.0004)`
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error: aborting due to 5 previous errors
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‎tests/ui/mul_add_fixable.fixed

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// run-rustfix
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#![warn(clippy::manual_mul_add)]
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#![allow(unused_variables)]
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fn mul_add_test() {
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let a: f64 = 1234.567;
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let b: f64 = 45.67834;
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let c: f64 = 0.0004;
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// Auto-fixable examples
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let test1 = a.mul_add(b, c);
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let test2 = a.mul_add(b, c);
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let test3 = a.mul_add(b, c);
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let test4 = a.mul_add(b, c);
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let test5 = a.mul_add(b, c).mul_add(a.mul_add(b, c), a.mul_add(b, c)) + c;
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let test6 = 1234.567_f64.mul_add(45.67834_f64, 0.0004_f64);
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}
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fn main() {
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mul_add_test();
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}

‎tests/ui/mul_add_fixable.rs

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// run-rustfix
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#![warn(clippy::manual_mul_add)]
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#![allow(unused_variables)]
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fn mul_add_test() {
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let a: f64 = 1234.567;
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let b: f64 = 45.67834;
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let c: f64 = 0.0004;
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// Auto-fixable examples
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let test1 = a * b + c;
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let test2 = c + a * b;
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let test3 = (a * b) + c;
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let test4 = c + (a * b);
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let test5 = a.mul_add(b, c) * a.mul_add(b, c) + a.mul_add(b, c) + c;
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let test6 = 1234.567_f64 * 45.67834_f64 + 0.0004_f64;
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}
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fn main() {
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mul_add_test();
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}

‎tests/ui/mul_add_fixable.stderr

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error: consider using mul_add() for better numerical precision
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--> $DIR/mul_add_fixable.rs:12:17
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|
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LL | let test1 = a * b + c;
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| ^^^^^^^^^ help: try: `a.mul_add(b, c)`
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|
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= note: `-D clippy::manual-mul-add` implied by `-D warnings`
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error: consider using mul_add() for better numerical precision
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--> $DIR/mul_add_fixable.rs:13:17
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|
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LL | let test2 = c + a * b;
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| ^^^^^^^^^ help: try: `a.mul_add(b, c)`
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error: consider using mul_add() for better numerical precision
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--> $DIR/mul_add_fixable.rs:15:17
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|
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LL | let test3 = (a * b) + c;
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| ^^^^^^^^^^^ help: try: `a.mul_add(b, c)`
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error: consider using mul_add() for better numerical precision
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--> $DIR/mul_add_fixable.rs:16:17
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|
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LL | let test4 = c + (a * b);
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| ^^^^^^^^^^^ help: try: `a.mul_add(b, c)`
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error: consider using mul_add() for better numerical precision
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--> $DIR/mul_add_fixable.rs:18:17
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|
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LL | let test5 = a.mul_add(b, c) * a.mul_add(b, c) + a.mul_add(b, c) + c;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `a.mul_add(b, c).mul_add(a.mul_add(b, c), a.mul_add(b, c))`
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error: consider using mul_add() for better numerical precision
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--> $DIR/mul_add_fixable.rs:19:17
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|
36+
LL | let test6 = 1234.567_f64 * 45.67834_f64 + 0.0004_f64;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `1234.567_f64.mul_add(45.67834_f64, 0.0004_f64)`
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error: aborting due to 6 previous errors
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