1 files changed, 131 insertions, 0 deletions
diff --git a/lib/std/math/isinf.zig b/lib/std/math/isinf.zig
new file mode 100644
index 0000000000..37934f4cf4
--- /dev/null
+++ b/lib/std/math/isinf.zig
@@ -0,0 +1,131 @@
+const std = @import("../std.zig");
+const math = std.math;
+const expect = std.testing.expect;
+const maxInt = std.math.maxInt;
+
+/// Returns whether x is an infinity, ignoring sign.
+pub fn isInf(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);
+        },
+        f128 => {
+            const bits = @bitCast(u128, x);
+            return bits & (maxInt(u128) >> 1) == (0x7FFF << 112);
+        },
+        else => {
+            @compileError("isInf not implemented for " ++ @typeName(T));
+        },
+    }
+}
+
+/// Returns whether x is an infinity with a positive sign.
+pub fn isPositiveInf(x: var) bool {
+    const T = @typeOf(x);
+    switch (T) {
+        f16 => {
+            return @bitCast(u16, x) == 0x7C00;
+        },
+        f32 => {
+            return @bitCast(u32, x) == 0x7F800000;
+        },
+        f64 => {
+            return @bitCast(u64, x) == 0x7FF << 52;
+        },
+        f128 => {
+            return @bitCast(u128, x) == 0x7FFF << 112;
+        },
+        else => {
+            @compileError("isPositiveInf not implemented for " ++ @typeName(T));
+        },
+    }
+}
+
+/// Returns whether x is an infinity with a negative sign.
+pub fn isNegativeInf(x: var) bool {
+    const T = @typeOf(x);
+    switch (T) {
+        f16 => {
+            return @bitCast(u16, x) == 0xFC00;
+        },
+        f32 => {
+            return @bitCast(u32, x) == 0xFF800000;
+        },
+        f64 => {
+            return @bitCast(u64, x) == 0xFFF << 52;
+        },
+        f128 => {
+            return @bitCast(u128, x) == 0xFFFF << 112;
+        },
+        else => {
+            @compileError("isNegativeInf not implemented for " ++ @typeName(T));
+        },
+    }
+}
+
+test "math.isInf" {
+    expect(!isInf(f16(0.0)));
+    expect(!isInf(f16(-0.0)));
+    expect(!isInf(f32(0.0)));
+    expect(!isInf(f32(-0.0)));
+    expect(!isInf(f64(0.0)));
+    expect(!isInf(f64(-0.0)));
+    expect(!isInf(f128(0.0)));
+    expect(!isInf(f128(-0.0)));
+    expect(isInf(math.inf(f16)));
+    expect(isInf(-math.inf(f16)));
+    expect(isInf(math.inf(f32)));
+    expect(isInf(-math.inf(f32)));
+    expect(isInf(math.inf(f64)));
+    expect(isInf(-math.inf(f64)));
+    expect(isInf(math.inf(f128)));
+    expect(isInf(-math.inf(f128)));
+}
+
+test "math.isPositiveInf" {
+    expect(!isPositiveInf(f16(0.0)));
+    expect(!isPositiveInf(f16(-0.0)));
+    expect(!isPositiveInf(f32(0.0)));
+    expect(!isPositiveInf(f32(-0.0)));
+    expect(!isPositiveInf(f64(0.0)));
+    expect(!isPositiveInf(f64(-0.0)));
+    expect(!isPositiveInf(f128(0.0)));
+    expect(!isPositiveInf(f128(-0.0)));
+    expect(isPositiveInf(math.inf(f16)));
+    expect(!isPositiveInf(-math.inf(f16)));
+    expect(isPositiveInf(math.inf(f32)));
+    expect(!isPositiveInf(-math.inf(f32)));
+    expect(isPositiveInf(math.inf(f64)));
+    expect(!isPositiveInf(-math.inf(f64)));
+    expect(isPositiveInf(math.inf(f128)));
+    expect(!isPositiveInf(-math.inf(f128)));
+}
+
+test "math.isNegativeInf" {
+    expect(!isNegativeInf(f16(0.0)));
+    expect(!isNegativeInf(f16(-0.0)));
+    expect(!isNegativeInf(f32(0.0)));
+    expect(!isNegativeInf(f32(-0.0)));
+    expect(!isNegativeInf(f64(0.0)));
+    expect(!isNegativeInf(f64(-0.0)));
+    expect(!isNegativeInf(f128(0.0)));
+    expect(!isNegativeInf(f128(-0.0)));
+    expect(!isNegativeInf(math.inf(f16)));
+    expect(isNegativeInf(-math.inf(f16)));
+    expect(!isNegativeInf(math.inf(f32)));
+    expect(isNegativeInf(-math.inf(f32)));
+    expect(!isNegativeInf(math.inf(f64)));
+    expect(isNegativeInf(-math.inf(f64)));
+    expect(!isNegativeInf(math.inf(f128)));
+    expect(isNegativeInf(-math.inf(f128)));
+}