add std.math f16 floor support

refs #1122

std/math/floor.zig

@@ -12,12 +12,47 @@ const math = std.math;
 pub fn floor(x: var) @typeOf(x) {
     const T = @typeOf(x);
     return switch (T) {
+        f16 => floor16(x),
         f32 => floor32(x),
         f64 => floor64(x),
         else => @compileError("floor not implemented for " ++ @typeName(T)),
     };
 }
 
+fn floor16(x: f16) f16 {
+    var u = @bitCast(u16, x);
+    const e = @intCast(i16, (u >> 10) & 31) - 15;
+    var m: u16 = undefined;
+
+    // TODO: Shouldn't need this explicit check.
+    if (x == 0.0) {
+        return x;
+    }
+
+    if (e >= 10) {
+        return x;
+    }
+
+    if (e >= 0) {
+        m = u16(1023) >> @intCast(u4, e);
+        if (u & m == 0) {
+            return x;
+        }
+        math.forceEval(x + 0x1.0p120);
+        if (u >> 15 != 0) {
+            u += m;
+        }
+        return @bitCast(f16, u & ~m);
+    } else {
+        math.forceEval(x + 0x1.0p120);
+        if (u >> 15 == 0) {
+            return 0.0;
+        } else {
+            return -1.0;
+        }
+    }
+}
+
 fn floor32(x: f32) f32 {
     var u = @bitCast(u32, x);
     const e = @intCast(i32, (u >> 23) & 0xFF) - 0x7F;
@@ -84,10 +119,17 @@ fn floor64(x: f64) f64 {
 }
 
 test "math.floor" {
+    assert(floor(f16(1.3)) == floor16(1.3));
     assert(floor(f32(1.3)) == floor32(1.3));
     assert(floor(f64(1.3)) == floor64(1.3));
 }
 
+test "math.floor16" {
+    assert(floor16(1.3) == 1.0);
+    assert(floor16(-1.3) == -2.0);
+    assert(floor16(0.2) == 0.0);
+}
+
 test "math.floor32" {
     assert(floor32(1.3) == 1.0);
     assert(floor32(-1.3) == -2.0);
@@ -100,6 +142,14 @@ test "math.floor64" {
     assert(floor64(0.2) == 0.0);
 }
 
+test "math.floor16.special" {
+    assert(floor16(0.0) == 0.0);
+    assert(floor16(-0.0) == -0.0);
+    assert(math.isPositiveInf(floor16(math.inf(f16))));
+    assert(math.isNegativeInf(floor16(-math.inf(f16))));
+    assert(math.isNan(floor16(math.nan(f16))));
+}
+
 test "math.floor32.special" {
     assert(floor32(0.0) == 0.0);
     assert(floor32(-0.0) == -0.0);

std/math/index.zig

@@ -56,6 +56,11 @@ pub fn approxEq(comptime T: type, x: T, y: T, epsilon: T) bool {
 pub fn forceEval(value: var) void {
     const T = @typeOf(value);
     switch (T) {
+        f16 => {
+            var x: f16 = undefined;
+            const p = @ptrCast(*volatile f16, &x);
+            p.* = x;
+        },
         f32 => {
             var x: f32 = undefined;
             const p = @ptrCast(*volatile f32, &x);