1 files changed, 41 insertions, 0 deletions
diff --git a/lib/std/math/isfinite.zig b/lib/std/math/isfinite.zig
new file mode 100644
index 0000000000..99eba668f9
--- /dev/null
+++ b/lib/std/math/isfinite.zig
@@ -0,0 +1,41 @@
+const std = @import("../std.zig");
+const math = std.math;
+const expect = std.testing.expect;
+const maxInt = std.math.maxInt;
+
+/// Returns whether x is a finite value.
+pub fn isFinite(x: var) bool {
+    const T = @typeOf(x);
+    switch (T) {
+        f16 => {
+            const bits = @bitCast(u16, x);
+            return bits & 0x7FFF < 0x7C00;
+        },
+        f32 => {
+            const bits = @bitCast(u32, x);
+            return bits & 0x7FFFFFFF < 0x7F800000;
+        },
+        f64 => {
+            const bits = @bitCast(u64, x);
+            return bits & (maxInt(u64) >> 1) < (0x7FF << 52);
+        },
+        else => {
+            @compileError("isFinite not implemented for " ++ @typeName(T));
+        },
+    }
+}
+
+test "math.isFinite" {
+    expect(isFinite(f16(0.0)));
+    expect(isFinite(f16(-0.0)));
+    expect(isFinite(f32(0.0)));
+    expect(isFinite(f32(-0.0)));
+    expect(isFinite(f64(0.0)));
+    expect(isFinite(f64(-0.0)));
+    expect(!isFinite(math.inf(f16)));
+    expect(!isFinite(-math.inf(f16)));
+    expect(!isFinite(math.inf(f32)));
+    expect(!isFinite(-math.inf(f32)));
+    expect(!isFinite(math.inf(f64)));
+    expect(!isFinite(-math.inf(f64)));
+}