1 files changed, 171 insertions, 0 deletions
diff --git a/lib/std/math/floor.zig b/lib/std/math/floor.zig
new file mode 100644
index 0000000000..e5ff2b1fc1
--- /dev/null
+++ b/lib/std/math/floor.zig
@@ -0,0 +1,171 @@
+// Ported from musl, which is licensed under the MIT license:
+// https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT
+//
+// https://git.musl-libc.org/cgit/musl/tree/src/math/floorf.c
+// https://git.musl-libc.org/cgit/musl/tree/src/math/floor.c
+
+const builtin = @import("builtin");
+const expect = std.testing.expect;
+const std = @import("../std.zig");
+const math = std.math;
+
+/// Returns the greatest integer value less than or equal to x.
+///
+/// Special Cases:
+///  - floor(+-0)   = +-0
+///  - floor(+-inf) = +-inf
+///  - floor(nan)   = nan
+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;
+    var m: u32 = undefined;
+
+    // TODO: Shouldn't need this explicit check.
+    if (x == 0.0) {
+        return x;
+    }
+
+    if (e >= 23) {
+        return x;
+    }
+
+    if (e >= 0) {
+        m = u32(0x007FFFFF) >> @intCast(u5, e);
+        if (u & m == 0) {
+            return x;
+        }
+        math.forceEval(x + 0x1.0p120);
+        if (u >> 31 != 0) {
+            u += m;
+        }
+        return @bitCast(f32, u & ~m);
+    } else {
+        math.forceEval(x + 0x1.0p120);
+        if (u >> 31 == 0) {
+            return 0.0;
+        } else {
+            return -1.0;
+        }
+    }
+}
+
+fn floor64(x: f64) f64 {
+    const u = @bitCast(u64, x);
+    const e = (u >> 52) & 0x7FF;
+    var y: f64 = undefined;
+
+    if (e >= 0x3FF + 52 or x == 0) {
+        return x;
+    }
+
+    if (u >> 63 != 0) {
+        y = x - math.f64_toint + math.f64_toint - x;
+    } else {
+        y = x + math.f64_toint - math.f64_toint - x;
+    }
+
+    if (e <= 0x3FF - 1) {
+        math.forceEval(y);
+        if (u >> 63 != 0) {
+            return -1.0;
+        } else {
+            return 0.0;
+        }
+    } else if (y > 0) {
+        return x + y - 1;
+    } else {
+        return x + y;
+    }
+}
+
+test "math.floor" {
+    expect(floor(f16(1.3)) == floor16(1.3));
+    expect(floor(f32(1.3)) == floor32(1.3));
+    expect(floor(f64(1.3)) == floor64(1.3));
+}
+
+test "math.floor16" {
+    expect(floor16(1.3) == 1.0);
+    expect(floor16(-1.3) == -2.0);
+    expect(floor16(0.2) == 0.0);
+}
+
+test "math.floor32" {
+    expect(floor32(1.3) == 1.0);
+    expect(floor32(-1.3) == -2.0);
+    expect(floor32(0.2) == 0.0);
+}
+
+test "math.floor64" {
+    expect(floor64(1.3) == 1.0);
+    expect(floor64(-1.3) == -2.0);
+    expect(floor64(0.2) == 0.0);
+}
+
+test "math.floor16.special" {
+    expect(floor16(0.0) == 0.0);
+    expect(floor16(-0.0) == -0.0);
+    expect(math.isPositiveInf(floor16(math.inf(f16))));
+    expect(math.isNegativeInf(floor16(-math.inf(f16))));
+    expect(math.isNan(floor16(math.nan(f16))));
+}
+
+test "math.floor32.special" {
+    expect(floor32(0.0) == 0.0);
+    expect(floor32(-0.0) == -0.0);
+    expect(math.isPositiveInf(floor32(math.inf(f32))));
+    expect(math.isNegativeInf(floor32(-math.inf(f32))));
+    expect(math.isNan(floor32(math.nan(f32))));
+}
+
+test "math.floor64.special" {
+    expect(floor64(0.0) == 0.0);
+    expect(floor64(-0.0) == -0.0);
+    expect(math.isPositiveInf(floor64(math.inf(f64))));
+    expect(math.isNegativeInf(floor64(-math.inf(f64))));
+    expect(math.isNan(floor64(math.nan(f64))));
+}