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Detect usage of (x + 1).ln() and suggest x.ln_1p() instead
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@krishna-veerareddy
krishna-veerareddy committed Feb 24, 2020
1 parent a60ae5d commit de07c84
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Showing 3 changed files with 84 additions and 24 deletions.
14 changes: 8 additions & 6 deletions clippy_lints/src/floating_point_arithmetic.rs
View file
Expand Up @@ -94,24 +94,26 @@ fn check_log_base(cx: &LateContext<'_, '_>, expr: &Expr, args: &HirVec<Expr>) {
}
}

// TODO: Lint expressions of the form `(x + 1).ln()` and `(x + y).ln()`
// where y > 1 and suggest usage of `(x + (y - 1)).ln_1p()` instead
// TODO: Lint expressions of the form `(x + y).ln()` where y > 1 and
// suggest usage of `(x + (y - 1)).ln_1p()` instead
fn check_ln1p(cx: &LateContext<'_, '_>, expr: &Expr, args: &HirVec<Expr>) {
if_chain! {
if let ExprKind::Binary(op, ref lhs, ref rhs) = &args[0].kind;
if op.node == BinOpKind::Add;
if let Some((value, _)) = constant(cx, cx.tables, lhs);
if F32(1.0) == value || F64(1.0) == value;
then {
let arg = sugg::Sugg::hir(cx, rhs, "..").maybe_par();
let recv = match (constant(cx, cx.tables, lhs), constant(cx, cx.tables, rhs)) {
(Some((value, _)), _) if F32(1.0) == value || F64(1.0) == value => rhs,
(_, Some((value, _))) if F32(1.0) == value || F64(1.0) == value => lhs,
_ => return,
};

span_lint_and_sugg(
cx,
FLOATING_POINT_IMPROVEMENTS,
expr.span,
"ln(1 + x) can be computed more accurately",
"consider using",
format!("{}.ln_1p()", arg),
format!("{}.ln_1p()", sugg::Sugg::hir(cx, recv, "..").maybe_par()),
Applicability::MachineApplicable,
);
}
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14 changes: 12 additions & 2 deletions tests/ui/floating_point_log.rs
View file
Expand Up @@ -25,18 +25,28 @@ fn check_ln1p() {
let _ = (1.0 + x.powi(2)).ln();
let _ = (1.0 + x.powi(2) * 2.0).ln();
let _ = (1.0 + (std::f32::consts::E - 1.0)).ln();
// Cases where the lint shouldn't be applied
let _ = (x + 1.0).ln();
let _ = (x.powi(2) + 1.0).ln();
let _ = (x + 2.0 + 1.0).ln();
let _ = (x * 2.0 + 1.0).ln();
// Cases where the lint shouldn't be applied
let _ = (1.0 + x + 2.0).ln();
let _ = (x + 1.0 + 2.0).ln();
let _ = (x + 1.0 * 2.0).ln();
let _ = (1.0 + x - 2.0).ln();

let x = 1f64;
let _ = (1.0 + x).ln();
let _ = (1.0 + x * 2.0).ln();
let _ = (1.0 + x.powi(2)).ln();
// Cases where the lint shouldn't be applied
let _ = (x + 1.0).ln();
let _ = (x.powi(2) + 1.0).ln();
let _ = (x + 2.0 + 1.0).ln();
let _ = (x * 2.0 + 1.0).ln();
// Cases where the lint shouldn't be applied
let _ = (1.0 + x + 2.0).ln();
let _ = (x + 1.0 + 2.0).ln();
let _ = (x + 1.0 * 2.0).ln();
let _ = (1.0 + x - 2.0).ln();
}

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80 changes: 64 additions & 16 deletions tests/ui/floating_point_log.stderr
View file
Expand Up @@ -79,94 +79,142 @@ LL | let _ = (1.0 + (std::f32::consts::E - 1.0)).ln();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `((std::f32::consts::E - 1.0)).ln_1p()`

error: ln(1 + x) can be computed more accurately
--> $DIR/floating_point_log.rs:34:13
--> $DIR/floating_point_log.rs:28:13
|
LL | let _ = (x + 1.0).ln();
| ^^^^^^^^^^^^^^ help: consider using: `x.ln_1p()`

error: ln(1 + x) can be computed more accurately
--> $DIR/floating_point_log.rs:29:13
|
LL | let _ = (x.powi(2) + 1.0).ln();
| ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.powi(2).ln_1p()`

error: ln(1 + x) can be computed more accurately
--> $DIR/floating_point_log.rs:30:13
|
LL | let _ = (x + 2.0 + 1.0).ln();
| ^^^^^^^^^^^^^^^^^^^^ help: consider using: `(x + 2.0).ln_1p()`

error: ln(1 + x) can be computed more accurately
--> $DIR/floating_point_log.rs:31:13
|
LL | let _ = (x * 2.0 + 1.0).ln();
| ^^^^^^^^^^^^^^^^^^^^ help: consider using: `(x * 2.0).ln_1p()`

error: ln(1 + x) can be computed more accurately
--> $DIR/floating_point_log.rs:39:13
|
LL | let _ = (1.0 + x).ln();
| ^^^^^^^^^^^^^^ help: consider using: `x.ln_1p()`

error: ln(1 + x) can be computed more accurately
--> $DIR/floating_point_log.rs:35:13
--> $DIR/floating_point_log.rs:40:13
|
LL | let _ = (1.0 + x * 2.0).ln();
| ^^^^^^^^^^^^^^^^^^^^ help: consider using: `(x * 2.0).ln_1p()`

error: ln(1 + x) can be computed more accurately
--> $DIR/floating_point_log.rs:36:13
--> $DIR/floating_point_log.rs:41:13
|
LL | let _ = (1.0 + x.powi(2)).ln();
| ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.powi(2).ln_1p()`

error: ln(1 + x) can be computed more accurately
--> $DIR/floating_point_log.rs:42:13
|
LL | let _ = (x + 1.0).ln();
| ^^^^^^^^^^^^^^ help: consider using: `x.ln_1p()`

error: ln(1 + x) can be computed more accurately
--> $DIR/floating_point_log.rs:43:13
|
LL | let _ = (x.powi(2) + 1.0).ln();
| ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.powi(2).ln_1p()`

error: ln(1 + x) can be computed more accurately
--> $DIR/floating_point_log.rs:44:13
|
LL | let _ = (x + 2.0 + 1.0).ln();
| ^^^^^^^^^^^^^^^^^^^^ help: consider using: `(x + 2.0).ln_1p()`

error: ln(1 + x) can be computed more accurately
--> $DIR/floating_point_log.rs:45:13
|
LL | let _ = (x * 2.0 + 1.0).ln();
| ^^^^^^^^^^^^^^^^^^^^ help: consider using: `(x * 2.0).ln_1p()`

error: x.log(b) / y.log(b) can be reduced to x.log(y)
--> $DIR/floating_point_log.rs:48:13
--> $DIR/floating_point_log.rs:58:13
|
LL | let _ = x.log2() / y.log2();
| ^^^^^^^^^^^^^^^^^^^ help: consider using: `x.log(y)`

error: x.log(b) / y.log(b) can be reduced to x.log(y)
--> $DIR/floating_point_log.rs:49:13
--> $DIR/floating_point_log.rs:59:13
|
LL | let _ = x.log10() / y.log10();
| ^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.log(y)`

error: x.log(b) / y.log(b) can be reduced to x.log(y)
--> $DIR/floating_point_log.rs:50:13
--> $DIR/floating_point_log.rs:60:13
|
LL | let _ = x.ln() / y.ln();
| ^^^^^^^^^^^^^^^ help: consider using: `x.log(y)`

error: x.log(b) / y.log(b) can be reduced to x.log(y)
--> $DIR/floating_point_log.rs:51:13
--> $DIR/floating_point_log.rs:61:13
|
LL | let _ = x.log(4.0) / y.log(4.0);
| ^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.log(y)`

error: x.log(b) / y.log(b) can be reduced to x.log(y)
--> $DIR/floating_point_log.rs:52:13
--> $DIR/floating_point_log.rs:62:13
|
LL | let _ = x.log(b) / y.log(b);
| ^^^^^^^^^^^^^^^^^^^ help: consider using: `x.log(y)`

error: x.log(b) / y.log(b) can be reduced to x.log(y)
--> $DIR/floating_point_log.rs:54:13
--> $DIR/floating_point_log.rs:64:13
|
LL | let _ = x.log(b) / 2f32.log(b);
| ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.log2()`

error: x.log(b) / y.log(b) can be reduced to x.log(y)
--> $DIR/floating_point_log.rs:60:13
--> $DIR/floating_point_log.rs:70:13
|
LL | let _ = x.log2() / y.log2();
| ^^^^^^^^^^^^^^^^^^^ help: consider using: `x.log(y)`

error: x.log(b) / y.log(b) can be reduced to x.log(y)
--> $DIR/floating_point_log.rs:61:13
--> $DIR/floating_point_log.rs:71:13
|
LL | let _ = x.log10() / y.log10();
| ^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.log(y)`

error: x.log(b) / y.log(b) can be reduced to x.log(y)
--> $DIR/floating_point_log.rs:62:13
--> $DIR/floating_point_log.rs:72:13
|
LL | let _ = x.ln() / y.ln();
| ^^^^^^^^^^^^^^^ help: consider using: `x.log(y)`

error: x.log(b) / y.log(b) can be reduced to x.log(y)
--> $DIR/floating_point_log.rs:63:13
--> $DIR/floating_point_log.rs:73:13
|
LL | let _ = x.log(4.0) / y.log(4.0);
| ^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.log(y)`

error: x.log(b) / y.log(b) can be reduced to x.log(y)
--> $DIR/floating_point_log.rs:64:13
--> $DIR/floating_point_log.rs:74:13
|
LL | let _ = x.log(b) / y.log(b);
| ^^^^^^^^^^^^^^^^^^^ help: consider using: `x.log(y)`

error: x.log(b) / y.log(b) can be reduced to x.log(y)
--> $DIR/floating_point_log.rs:66:13
--> $DIR/floating_point_log.rs:76:13
|
LL | let _ = x.log(b) / 2f64.log(b);
| ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.log2()`

error: aborting due to 28 previous errors
error: aborting due to 36 previous errors

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