From ca444e6191138e6f9977cf2fbceb071134ed6aff Mon Sep 17 00:00:00 2001
From: Ben Noordhuis <info@bnoordhuis.nl>
Date: Sat, 30 Jun 2018 01:44:54 +0200
Subject: [PATCH] add std.math f16 copysign support

refs #1122
---
 std/math/copysign.zig | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/std/math/copysign.zig b/std/math/copysign.zig
index 4ca8f82f4..8c71dcb0b 100644
--- a/std/math/copysign.zig
+++ b/std/math/copysign.zig
@@ -4,12 +4,22 @@ const assert = std.debug.assert;
 
 pub fn copysign(comptime T: type, x: T, y: T) T {
     return switch (T) {
+        f16 => copysign16(x, y),
         f32 => copysign32(x, y),
         f64 => copysign64(x, y),
         else => @compileError("copysign not implemented for " ++ @typeName(T)),
     };
 }
 
+fn copysign16(x: f16, y: f16) f16 {
+    const ux = @bitCast(u16, x);
+    const uy = @bitCast(u16, y);
+
+    const h1 = ux & (@maxValue(u16) / 2);
+    const h2 = uy & (u16(1) << 15);
+    return @bitCast(f16, h1 | h2);
+}
+
 fn copysign32(x: f32, y: f32) f32 {
     const ux = @bitCast(u32, x);
     const uy = @bitCast(u32, y);
@@ -29,10 +39,18 @@ fn copysign64(x: f64, y: f64) f64 {
 }
 
 test "math.copysign" {
+    assert(copysign(f16, 1.0, 1.0) == copysign16(1.0, 1.0));
     assert(copysign(f32, 1.0, 1.0) == copysign32(1.0, 1.0));
     assert(copysign(f64, 1.0, 1.0) == copysign64(1.0, 1.0));
 }
 
+test "math.copysign16" {
+    assert(copysign16(5.0, 1.0) == 5.0);
+    assert(copysign16(5.0, -1.0) == -5.0);
+    assert(copysign16(-5.0, -1.0) == -5.0);
+    assert(copysign16(-5.0, 1.0) == 5.0);
+}
+
 test "math.copysign32" {
     assert(copysign32(5.0, 1.0) == 5.0);
     assert(copysign32(5.0, -1.0) == -5.0);