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math.fabs: simplify implementation, add tests

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viri 2022-04-01 15:18:25 -06:00 committed by Isaac Freund
parent 2f6ee4a97d
commit cb019b80ac
1 changed files with 26 additions and 82 deletions
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108
lib/std/math/fabs.zig
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@ -1,13 +1,6 @@
// Ported from musl, which is licensed under the MIT license:
// https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT
//
// https://git.musl-libc.org/cgit/musl/tree/src/math/fabsf.c
// https://git.musl-libc.org/cgit/musl/tree/src/math/fabs.c
const std = @import("../std.zig");
const math = std.math;
const expect = std.testing.expect;
const maxInt = std.math.maxInt;
/// Returns the absolute value of x.
///
@ -16,86 +9,37 @@ const maxInt = std.math.maxInt;
/// - fabs(nan) = nan
pub fn fabs(x: anytype) @TypeOf(x) {
const T = @TypeOf(x);
return switch (T) {
f16 => fabs16(x),
f32 => fabs32(x),
f64 => fabs64(x),
f128 => fabs128(x),
else => @compileError("fabs not implemented for " ++ @typeName(T)),
};
}
const TBits = std.meta.Int(.unsigned, @bitSizeOf(T));
if (@typeInfo(T) != .Float) {
@compileError("fabs not implemented for " ++ @typeName(T));
}
fn fabs16(x: f16) f16 {
var u = @bitCast(u16, x);
u &= maxInt(u16) >> 1;
return @bitCast(f16, u);
}
const float_bits = @bitCast(TBits, x);
const remove_sign = ~@as(TBits, 0) >> 1;
fn fabs32(x: f32) f32 {
var u = @bitCast(u32, x);
u &= maxInt(u32) >> 1;
return @bitCast(f32, u);
}
fn fabs64(x: f64) f64 {
var u = @bitCast(u64, x);
u &= maxInt(u64) >> 1;
return @bitCast(f64, u);
}
fn fabs128(x: f128) f128 {
var u = @bitCast(u128, x);
u &= maxInt(u128) >> 1;
return @bitCast(f128, u);
return @bitCast(T, float_bits & remove_sign);
}
test "math.fabs" {
try expect(fabs(@as(f16, 1.0)) == fabs16(1.0));
try expect(fabs(@as(f32, 1.0)) == fabs32(1.0));
try expect(fabs(@as(f64, 1.0)) == fabs64(1.0));
try expect(fabs(@as(f128, 1.0)) == fabs128(1.0));
}
// TODO add support for f80 & c_longdouble here
inline for ([_]type{ f16, f32, f64, f128 }) |T| {
// normals
try expect(fabs(@as(T, 1.0)) == 1.0);
try expect(fabs(@as(T, -1.0)) == 1.0);
try expect(fabs(math.floatMin(T)) == math.floatMin(T));
try expect(fabs(-math.floatMin(T)) == math.floatMin(T));
try expect(fabs(math.floatMax(T)) == math.floatMax(T));
try expect(fabs(-math.floatMax(T)) == math.floatMax(T));
test "math.fabs16" {
try expect(fabs16(1.0) == 1.0);
try expect(fabs16(-1.0) == 1.0);
}
// subnormals
try expect(fabs(@as(T, 0.0)) == 0.0);
try expect(fabs(@as(T, -0.0)) == 0.0);
try expect(fabs(math.floatTrueMin(T)) == math.floatTrueMin(T));
try expect(fabs(-math.floatTrueMin(T)) == math.floatTrueMin(T));
test "math.fabs32" {
try expect(fabs32(1.0) == 1.0);
try expect(fabs32(-1.0) == 1.0);
}
test "math.fabs64" {
try expect(fabs64(1.0) == 1.0);
try expect(fabs64(-1.0) == 1.0);
}
test "math.fabs128" {
try expect(fabs128(1.0) == 1.0);
try expect(fabs128(-1.0) == 1.0);
}
test "math.fabs16.special" {
try expect(math.isPositiveInf(fabs(math.inf(f16))));
try expect(math.isPositiveInf(fabs(-math.inf(f16))));
try expect(math.isNan(fabs(math.nan(f16))));
}
test "math.fabs32.special" {
try expect(math.isPositiveInf(fabs(math.inf(f32))));
try expect(math.isPositiveInf(fabs(-math.inf(f32))));
try expect(math.isNan(fabs(math.nan(f32))));
}
test "math.fabs64.special" {
try expect(math.isPositiveInf(fabs(math.inf(f64))));
try expect(math.isPositiveInf(fabs(-math.inf(f64))));
try expect(math.isNan(fabs(math.nan(f64))));
}
test "math.fabs128.special" {
try expect(math.isPositiveInf(fabs(math.inf(f128))));
try expect(math.isPositiveInf(fabs(-math.inf(f128))));
try expect(math.isNan(fabs(math.nan(f128))));
// non-finite numbers
try expect(math.isPositiveInf(fabs(math.inf(T))));
try expect(math.isPositiveInf(fabs(-math.inf(T))));
try expect(math.isNan(fabs(math.nan(T))));
}
}