1 files changed, 35 insertions, 0 deletions
diff --git a/lib/std/math/expo2.zig b/lib/std/math/expo2.zig
new file mode 100644
index 0000000000..c00098a5a7
--- /dev/null
+++ b/lib/std/math/expo2.zig
@@ -0,0 +1,35 @@
+// 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/__expo2f.c
+// https://git.musl-libc.org/cgit/musl/tree/src/math/__expo2.c
+
+const math = @import("../math.zig");
+
+/// Returns exp(x) / 2 for x >= log(maxFloat(T)).
+pub fn expo2(x: var) @typeOf(x) {
+    const T = @typeOf(x);
+    return switch (T) {
+        f32 => expo2f(x),
+        f64 => expo2d(x),
+        else => @compileError("expo2 not implemented for " ++ @typeName(T)),
+    };
+}
+
+fn expo2f(x: f32) f32 {
+    const k: u32 = 235;
+    const kln2 = 0x1.45C778p+7;
+
+    const u = (0x7F + k / 2) << 23;
+    const scale = @bitCast(f32, u);
+    return math.exp(x - kln2) * scale * scale;
+}
+
+fn expo2d(x: f64) f64 {
+    const k: u32 = 2043;
+    const kln2 = 0x1.62066151ADD8BP+10;
+
+    const u = (0x3FF + k / 2) << 20;
+    const scale = @bitCast(f64, u64(u) << 32);
+    return math.exp(x - kln2) * scale * scale;
+}