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Merge pull request #413 from iKevinY/approx-const

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Compare float literals to stringified constants
This commit is contained in:
llogiq 2015-10-25 10:35:29 +01:00
commit d0a4d19fe3
2 changed files with 46 additions and 27 deletions
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71
src/approx_const.rs
View File

@ -1,5 +1,6 @@
use rustc::lint::*;
use rustc_front::hir::*;
use std::f64::consts as f64;
use utils::span_lint;
use syntax::ast::Lit_::*;
use syntax::ast::Lit;
@ -12,25 +13,24 @@ declare_lint! {
is found; suggests to use the constant"
}
// Tuples are of the form (name, lower_bound, upper_bound)
#[allow(approx_constant)]
const KNOWN_CONSTS : &'static [(&'static str, f64, f64)] = &[
("E", 2.7101, 2.7200),
("FRAC_1_PI", 0.31829, 0.31840),
("FRAC_1_SQRT_2", 0.7071, 0.7072),
("FRAC_2_PI", 0.6366, 0.6370),
("FRAC_2_SQRT_PI", 1.1283, 1.1284),
("FRAC_PI_2", 1.5707, 1.5708),
("FRAC_PI_3", 1.0471, 1.0472),
("FRAC_PI_4", 0.7853, 0.7854),
("FRAC_PI_6", 0.5235, 0.5236),
("FRAC_PI_8", 0.3926, 0.3927),
("LN_10", 2.302, 2.303),
("LN_2", 0.6931, 0.6932),
("LOG10_E", 0.4342, 0.4343),
("LOG2_E", 1.4426, 1.4427),
("PI", 3.140, 3.142),
("SQRT_2", 1.4142, 1.4143),
// Tuples are of the form (constant, name, min_digits)
const KNOWN_CONSTS : &'static [(f64, &'static str, usize)] = &[
(f64::E, "E", 4),
(f64::FRAC_1_PI, "FRAC_1_PI", 4),
(f64::FRAC_1_SQRT_2, "FRAC_1_SQRT_2", 5),
(f64::FRAC_2_PI, "FRAC_2_PI", 5),
(f64::FRAC_2_SQRT_PI, "FRAC_2_SQRT_PI", 5),
(f64::FRAC_PI_2, "FRAC_PI_2", 5),
(f64::FRAC_PI_3, "FRAC_PI_3", 5),
(f64::FRAC_PI_4, "FRAC_PI_4", 5),
(f64::FRAC_PI_6, "FRAC_PI_6", 5),
(f64::FRAC_PI_8, "FRAC_PI_8", 5),
(f64::LN_10, "LN_10", 5),
(f64::LN_2, "LN_2", 5),
(f64::LOG10_E, "LOG10_E", 5),
(f64::LOG2_E, "LOG2_E", 5),
(f64::PI, "PI", 3),
(f64::SQRT_2, "SQRT_2", 5),
];
#[derive(Copy,Clone)]
@ -52,22 +52,41 @@ impl LateLintPass for ApproxConstant {
fn check_lit(cx: &LateContext, lit: &Lit, e: &Expr) {
match lit.node {
LitFloat(ref str, TyF32) => check_known_consts(cx, e, str, "f32"),
LitFloat(ref str, TyF64) => check_known_consts(cx, e, str, "f64"),
LitFloatUnsuffixed(ref str) =>
check_known_consts(cx, e, str, "f{32, 64}"),
LitFloat(ref s, TyF32) => check_known_consts(cx, e, s, "f32"),
LitFloat(ref s, TyF64) => check_known_consts(cx, e, s, "f64"),
LitFloatUnsuffixed(ref s) =>
check_known_consts(cx, e, s, "f{32, 64}"),
_ => ()
}
}
fn check_known_consts(cx: &LateContext, e: &Expr, s: &str, module: &str) {
if let Ok(value) = s.parse::<f64>() {
for &(name, lower_bound, upper_bound) in KNOWN_CONSTS {
if (value >= lower_bound) && (value < upper_bound) {
if let Ok(_) = s.parse::<f64>() {
for &(constant, name, min_digits) in KNOWN_CONSTS {
if is_approx_const(constant, s, min_digits) {
span_lint(cx, APPROX_CONSTANT, e.span, &format!(
"approximate value of `{}::{}` found. \
Consider using it directly", module, &name));
return;
}
}
}
}
/// Returns false if the number of significant figures in `value` are
/// less than `min_digits`; otherwise, returns true if `value` is equal
/// to `constant`, rounded to the number of digits present in `value`.
fn is_approx_const(constant: f64, value: &str, min_digits: usize) -> bool {
if value.len() <= min_digits {
false
} else {
let round_const = format!("{:.*}", value.len() - 2, constant);
let mut trunc_const = constant.to_string();
if trunc_const.len() > value.len() {
trunc_const.truncate(value.len());
}
(value == round_const) || (value == trunc_const)
}
}

2
tests/compile-fail/approx_const.rs
View File

@ -42,7 +42,7 @@ fn main() {
let my_ln_2 = 0.6931471805599453; //~ERROR approximate value of `f{32, 64}::LN_2` found
let no_ln_2 = 0.693;
let my_log10_e = 0.43429448190325176; //~ERROR approximate value of `f{32, 64}::LOG10_E` found
let my_log10_e = 0.43429448190325182; //~ERROR approximate value of `f{32, 64}::LOG10_E` found
let no_log10_e = 0.434;
let my_log2_e = 1.4426950408889634; //~ERROR approximate value of `f{32, 64}::LOG2_E` found