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Consolidate the accuracy and efficiency lints

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Merge the accuracy and efficiency lints into a single lint that
checks for improvements to accuracy, efficiency and readability
of floating-point expressions.
This commit is contained in:
Krishna Veera Reddy 2019-12-14 20:10:23 -08:00 • committed by Krishna Sai Veera Reddy
parent c636c6a55b
commit 1f4f357bf5
6 changed files with 76 additions and 105 deletions
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89
clippy_lints/src/floating_point_arithmetic.rs
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@ -13,11 +13,12 @@ use std::f32::consts as f32_consts;
use std::f64::consts as f64_consts;
declare_clippy_lint! {
/// **What it does:** Looks for numerically unstable floating point
/// computations and suggests better alternatives.
/// **What it does:** Looks for floating-point expressions that
/// can be expressed using built-in methods to improve accuracy,
/// performance and/or succinctness.
///
/// **Why is this bad?** Numerically unstable floating point computations
/// cause rounding errors to magnify and distorts the results strongly.
/// **Why is this bad?** Negatively affects accuracy, performance
/// and/or readability.
///
/// **Known problems:** None
///
@ -26,59 +27,43 @@ declare_clippy_lint! {
/// ```rust
/// use std::f32::consts::E;
///
/// let a = 1f32.log(2.0);
/// let b = 1f32.log(10.0);
/// let c = 1f32.log(E);
/// let a = 3f32;
/// let _ = (2f32).powf(a);
/// let _ = E.powf(a);
/// let _ = a.powf(1.0 / 2.0);
/// let _ = a.powf(1.0 / 3.0);
/// let _ = a.log(2.0);
/// let _ = a.log(10.0);
/// let _ = a.log(E);
/// let _ = (1.0 + a).ln();
/// let _ = a.exp() - 1.0;
/// ```
///
/// is better expressed as
///
/// ```rust
/// let a = 1f32.log2();
/// let b = 1f32.log10();
/// let c = 1f32.ln();
/// ```
pub INACCURATE_FLOATING_POINT_COMPUTATION,
nursery,
"checks for numerically unstable floating point computations"
}
declare_clippy_lint! {
/// **What it does:** Looks for inefficient floating point computations
/// and suggests faster alternatives.
///
/// **Why is this bad?** Lower performance.
///
/// **Known problems:** None
///
/// **Example:**
///
/// ```rust
/// use std::f32::consts::E;
///
/// let a = (2f32).powf(3.0);
/// let c = E.powf(3.0);
/// let a = 3f32;
/// let _ = a.exp2();
/// let _ = a.exp();
/// let _ = a.sqrt();
/// let _ = a.cbrt();
/// let _ = a.log2();
/// let _ = a.log10();
/// let _ = a.ln();
/// let _ = a.ln_1p();
/// let _ = a.exp_m1();
/// ```
///
/// is better expressed as
///
/// ```rust
/// let a = (3f32).exp2();
/// let b = (3f32).exp();
/// ```
pub SLOW_FLOATING_POINT_COMPUTATION,
pub FLOATING_POINT_IMPROVEMENTS,
nursery,
"checks for inefficient floating point computations"
"looks for improvements to floating-point expressions"
}
declare_lint_pass!(FloatingPointArithmetic => [
INACCURATE_FLOATING_POINT_COMPUTATION,
SLOW_FLOATING_POINT_COMPUTATION
]);
declare_lint_pass!(FloatingPointArithmetic => [FLOATING_POINT_IMPROVEMENTS]);
fn check_log_base(cx: &LateContext<'_, '_>, expr: &Expr, args: &HirVec<Expr>) {
let recv = &args[0];
let arg = sugg::Sugg::hir(cx, recv, "..").maybe_par();
let arg = sugg::Sugg::hir(cx, &args[0], "..").maybe_par();
if let Some((value, _)) = constant(cx, cx.tables, &args[1]) {
let method;
@ -95,7 +80,7 @@ fn check_log_base(cx: &LateContext<'_, '_>, expr: &Expr, args: &HirVec<Expr>) {
span_lint_and_sugg(
cx,
INACCURATE_FLOATING_POINT_COMPUTATION,
FLOATING_POINT_IMPROVEMENTS,
expr.span,
"logarithm for bases 2, 10 and e can be computed more accurately",
"consider using",
@ -118,7 +103,7 @@ fn check_ln1p(cx: &LateContext<'_, '_>, expr: &Expr, args: &HirVec<Expr>) {
span_lint_and_sugg(
cx,
INACCURATE_FLOATING_POINT_COMPUTATION,
FLOATING_POINT_IMPROVEMENTS,
expr.span,
"ln(1 + x) can be computed more accurately",
"consider using",
@ -144,9 +129,9 @@ fn check_powf(cx: &LateContext<'_, '_>, expr: &Expr, args: &HirVec<Expr>) {
span_lint_and_sugg(
cx,
SLOW_FLOATING_POINT_COMPUTATION,
FLOATING_POINT_IMPROVEMENTS,
expr.span,
"exponent for bases 2 and e can be computed more efficiently",
"exponent for bases 2 and e can be computed more accurately",
"consider using",
format!("{}.{}()", sugg::Sugg::hir(cx, &args[1], "..").maybe_par(), method),
Applicability::MachineApplicable,
@ -159,10 +144,10 @@ fn check_powf(cx: &LateContext<'_, '_>, expr: &Expr, args: &HirVec<Expr>) {
let method;
if F32(1.0 / 2.0) == value || F64(1.0 / 2.0) == value {
help = "square-root of a number can be computer more efficiently";
help = "square-root of a number can be computed more efficiently and accurately";
method = "sqrt";
} else if F32(1.0 / 3.0) == value || F64(1.0 / 3.0) == value {
help = "cube-root of a number can be computer more efficiently";
help = "cube-root of a number can be computed more accurately";
method = "cbrt";
} else {
return;
@ -170,7 +155,7 @@ fn check_powf(cx: &LateContext<'_, '_>, expr: &Expr, args: &HirVec<Expr>) {
span_lint_and_sugg(
cx,
SLOW_FLOATING_POINT_COMPUTATION,
FLOATING_POINT_IMPROVEMENTS,
expr.span,
help,
"consider using",
@ -194,7 +179,7 @@ fn check_expm1(cx: &LateContext<'_, '_>, expr: &Expr) {
then {
span_lint_and_sugg(
cx,
INACCURATE_FLOATING_POINT_COMPUTATION,
FLOATING_POINT_IMPROVEMENTS,
expr.span,
"(e.pow(x) - 1) can be computed more accurately",
"consider using",