1 files changed, 38 insertions, 0 deletions
diff --git a/lib/std/math/isnormal.zig b/lib/std/math/isnormal.zig
new file mode 100644
index 0000000000..f8611ef805
--- /dev/null
+++ b/lib/std/math/isnormal.zig
@@ -0,0 +1,38 @@
+const std = @import("../std.zig");
+const math = std.math;
+const expect = std.testing.expect;
+const maxInt = std.math.maxInt;
+
+// Returns whether x has a normalized representation (i.e. integer part of mantissa is 1).
+pub fn isNormal(x: var) bool {
+    const T = @typeOf(x);
+    switch (T) {
+        f16 => {
+            const bits = @bitCast(u16, x);
+            return (bits + 1024) & 0x7FFF >= 2048;
+        },
+        f32 => {
+            const bits = @bitCast(u32, x);
+            return (bits + 0x00800000) & 0x7FFFFFFF >= 0x01000000;
+        },
+        f64 => {
+            const bits = @bitCast(u64, x);
+            return (bits + (1 << 52)) & (maxInt(u64) >> 1) >= (1 << 53);
+        },
+        else => {
+            @compileError("isNormal not implemented for " ++ @typeName(T));
+        },
+    }
+}
+
+test "math.isNormal" {
+    expect(!isNormal(math.nan(f16)));
+    expect(!isNormal(math.nan(f32)));
+    expect(!isNormal(math.nan(f64)));
+    expect(!isNormal(f16(0)));
+    expect(!isNormal(f32(0)));
+    expect(!isNormal(f64(0)));
+    expect(isNormal(f16(1.0)));
+    expect(isNormal(f32(1.0)));
+    expect(isNormal(f64(1.0)));
+}