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std: Fix complex ldexp implementation

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Two bugs in the implementation ported from musl made all the complex
functions relying on ldexp return incorrect results in some cases.

Spotted in #9047
This commit is contained in:
LemonBoy 2021-06-12 15:35:52 +02:00 committed by Veikka Tuominen
parent 0d022eb1d6
commit 44cdafd9d4
2 changed files with 40 additions and 14 deletions
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42
lib/std/math/complex/exp.zig
View File

@ -124,20 +124,42 @@ fn exp64(z: Complex(f64)) Complex(f64) {
}
}
const epsilon = 0.0001;
test "complex.cexp32" {
const a = Complex(f32).init(5, 3);
const c = exp(a);
const tolerance_f32 = math.sqrt(math.epsilon(f32));
try testing.expect(math.approxEqAbs(f32, c.re, -146.927917, epsilon));
try testing.expect(math.approxEqAbs(f32, c.im, 20.944065, epsilon));
{
const a = Complex(f32).init(5, 3);
const c = exp(a);
try testing.expectApproxEqRel(@as(f32, -1.46927917e+02), c.re, tolerance_f32);
try testing.expectApproxEqRel(@as(f32, 2.0944065e+01), c.im, tolerance_f32);
}
{
const a = Complex(f32).init(88.8, 0x1p-149);
const c = exp(a);
try testing.expectApproxEqAbs(math.inf(f32), c.re, tolerance_f32);
try testing.expectApproxEqAbs(@as(f32, 5.15088629e-07), c.im, tolerance_f32);
}
}
test "complex.cexp64" {
const a = Complex(f64).init(5, 3);
const c = exp(a);
const tolerance_f64 = math.sqrt(math.epsilon(f64));
try testing.expect(math.approxEqAbs(f64, c.re, -146.927917, epsilon));
try testing.expect(math.approxEqAbs(f64, c.im, 20.944065, epsilon));
{
const a = Complex(f64).init(5, 3);
const c = exp(a);
try testing.expectApproxEqRel(@as(f64, -1.469279139083189e+02), c.re, tolerance_f64);
try testing.expectApproxEqRel(@as(f64, 2.094406620874596e+01), c.im, tolerance_f64);
}
{
const a = Complex(f64).init(709.8, 0x1p-1074);
const c = exp(a);
try testing.expectApproxEqAbs(math.inf(f64), c.re, tolerance_f64);
try testing.expectApproxEqAbs(@as(f64, 9.036659362159884e-16), c.im, tolerance_f64);
}
}

12
lib/std/math/complex/ldexp.zig
View File

@ -13,6 +13,7 @@ const std = @import("../../std.zig");
const debug = std.debug;
const math = std.math;
const cmath = math.complex;
const testing = std.testing;
const Complex = cmath.Complex;
/// Returns exp(z) scaled to avoid overflow.
@ -48,7 +49,10 @@ fn ldexp_cexp32(z: Complex(f32), expt: i32) Complex(f32) {
const half_expt2 = exptf - half_expt1;
const scale2 = @bitCast(f32, (0x7f + half_expt2) << 23);
return Complex(f32).init(math.cos(z.im) * exp_x * scale1 * scale2, math.sin(z.im) * exp_x * scale1 * scale2);
return Complex(f32).init(
math.cos(z.im) * exp_x * scale1 * scale2,
math.sin(z.im) * exp_x * scale1 * scale2,
);
}
fn frexp_exp64(x: f64, expt: *i32) f64 {
@ -57,7 +61,7 @@ fn frexp_exp64(x: f64, expt: *i32) f64 {
const exp_x = math.exp(x - kln2);
const fx = @bitCast(u64, x);
const fx = @bitCast(u64, exp_x);
const hx = @intCast(u32, fx >> 32);
const lx = @truncate(u32, fx);
@ -73,10 +77,10 @@ fn ldexp_cexp64(z: Complex(f64), expt: i32) Complex(f64) {
const exptf = @as(i64, expt + ex_expt);
const half_expt1 = @divTrunc(exptf, 2);
const scale1 = @bitCast(f64, (0x3ff + half_expt1) << 20);
const scale1 = @bitCast(f64, (0x3ff + half_expt1) << (20 + 32));
const half_expt2 = exptf - half_expt1;
const scale2 = @bitCast(f64, (0x3ff + half_expt2) << 20);
const scale2 = @bitCast(f64, (0x3ff + half_expt2) << (20 + 32));
return Complex(f64).init(
math.cos(z.im) * exp_x * scale1 * scale2,