1 files changed, 101 insertions, 0 deletions
diff --git a/lib/std/math/fabs.zig b/lib/std/math/fabs.zig
new file mode 100644
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--- /dev/null
+++ b/lib/std/math/fabs.zig
@@ -0,0 +1,101 @@
+// 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.
+///
+/// Special Cases:
+///  - fabs(+-inf) = +inf
+///  - fabs(nan)   = nan
+pub fn fabs(x: var) @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)),
+    };
+}
+
+fn fabs16(x: f16) f16 {
+    var u = @bitCast(u16, x);
+    u &= 0x7FFF;
+    return @bitCast(f16, u);
+}
+
+fn fabs32(x: f32) f32 {
+    var u = @bitCast(u32, x);
+    u &= 0x7FFFFFFF;
+    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);
+}
+
+test "math.fabs" {
+    expect(fabs(f16(1.0)) == fabs16(1.0));
+    expect(fabs(f32(1.0)) == fabs32(1.0));
+    expect(fabs(f64(1.0)) == fabs64(1.0));
+    expect(fabs(f128(1.0)) == fabs128(1.0));
+}
+
+test "math.fabs16" {
+    expect(fabs16(1.0) == 1.0);
+    expect(fabs16(-1.0) == 1.0);
+}
+
+test "math.fabs32" {
+    expect(fabs32(1.0) == 1.0);
+    expect(fabs32(-1.0) == 1.0);
+}
+
+test "math.fabs64" {
+    expect(fabs64(1.0) == 1.0);
+    expect(fabs64(-1.0) == 1.0);
+}
+
+test "math.fabs128" {
+    expect(fabs128(1.0) == 1.0);
+    expect(fabs128(-1.0) == 1.0);
+}
+
+test "math.fabs16.special" {
+    expect(math.isPositiveInf(fabs(math.inf(f16))));
+    expect(math.isPositiveInf(fabs(-math.inf(f16))));
+    expect(math.isNan(fabs(math.nan(f16))));
+}
+
+test "math.fabs32.special" {
+    expect(math.isPositiveInf(fabs(math.inf(f32))));
+    expect(math.isPositiveInf(fabs(-math.inf(f32))));
+    expect(math.isNan(fabs(math.nan(f32))));
+}
+
+test "math.fabs64.special" {
+    expect(math.isPositiveInf(fabs(math.inf(f64))));
+    expect(math.isPositiveInf(fabs(-math.inf(f64))));
+    expect(math.isNan(fabs(math.nan(f64))));
+}
+
+test "math.fabs128.special" {
+    expect(math.isPositiveInf(fabs(math.inf(f128))));
+    expect(math.isPositiveInf(fabs(-math.inf(f128))));
+    expect(math.isNan(fabs(math.nan(f128))));
+}