144 lines
3.5 KiB
Zig
144 lines
3.5 KiB
Zig
// SPDX-License-Identifier: MIT
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// Copyright (c) 2015-2020 Zig Contributors
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// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
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// The MIT license requires this copyright notice to be included in all copies
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// and substantial portions of the software.
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// Ported from musl, which is licensed under the MIT license:
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// https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT
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//
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// https://git.musl-libc.org/cgit/musl/tree/src/math/ilogbf.c
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// https://git.musl-libc.org/cgit/musl/tree/src/math/ilogb.c
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const std = @import("../std.zig");
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const math = std.math;
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const expect = std.testing.expect;
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const maxInt = std.math.maxInt;
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const minInt = std.math.minInt;
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/// Returns the binary exponent of x as an integer.
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///
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/// Special Cases:
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/// - ilogb(+-inf) = maxInt(i32)
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/// - ilogb(0) = maxInt(i32)
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/// - ilogb(nan) = maxInt(i32)
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pub fn ilogb(x: anytype) i32 {
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const T = @TypeOf(x);
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return switch (T) {
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f32 => ilogb32(x),
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f64 => ilogb64(x),
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else => @compileError("ilogb not implemented for " ++ @typeName(T)),
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};
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}
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// NOTE: Should these be exposed publicly?
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const fp_ilogbnan = -1 - @as(i32, maxInt(u32) >> 1);
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const fp_ilogb0 = fp_ilogbnan;
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fn ilogb32(x: f32) i32 {
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var u = @bitCast(u32, x);
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var e = @intCast(i32, (u >> 23) & 0xFF);
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// TODO: We should be able to merge this with the lower check.
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if (math.isNan(x)) {
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return maxInt(i32);
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}
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if (e == 0) {
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u <<= 9;
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if (u == 0) {
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math.raiseInvalid();
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return fp_ilogb0;
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}
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// subnormal
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e = -0x7F;
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while (u >> 31 == 0) : (u <<= 1) {
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e -= 1;
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}
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return e;
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}
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if (e == 0xFF) {
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math.raiseInvalid();
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if (u << 9 != 0) {
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return fp_ilogbnan;
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} else {
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return maxInt(i32);
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}
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}
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return e - 0x7F;
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}
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fn ilogb64(x: f64) i32 {
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var u = @bitCast(u64, x);
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var e = @intCast(i32, (u >> 52) & 0x7FF);
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if (math.isNan(x)) {
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return maxInt(i32);
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}
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if (e == 0) {
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u <<= 12;
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if (u == 0) {
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math.raiseInvalid();
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return fp_ilogb0;
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}
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// subnormal
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e = -0x3FF;
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while (u >> 63 == 0) : (u <<= 1) {
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e -= 1;
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}
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return e;
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}
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if (e == 0x7FF) {
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math.raiseInvalid();
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if (u << 12 != 0) {
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return fp_ilogbnan;
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} else {
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return maxInt(i32);
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}
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}
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return e - 0x3FF;
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}
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test "math.ilogb" {
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expect(ilogb(@as(f32, 0.2)) == ilogb32(0.2));
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expect(ilogb(@as(f64, 0.2)) == ilogb64(0.2));
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}
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test "math.ilogb32" {
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expect(ilogb32(0.0) == fp_ilogb0);
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expect(ilogb32(0.5) == -1);
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expect(ilogb32(0.8923) == -1);
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expect(ilogb32(10.0) == 3);
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expect(ilogb32(-123984) == 16);
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expect(ilogb32(2398.23) == 11);
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}
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test "math.ilogb64" {
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expect(ilogb64(0.0) == fp_ilogb0);
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expect(ilogb64(0.5) == -1);
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expect(ilogb64(0.8923) == -1);
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expect(ilogb64(10.0) == 3);
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expect(ilogb64(-123984) == 16);
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expect(ilogb64(2398.23) == 11);
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}
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test "math.ilogb32.special" {
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expect(ilogb32(math.inf(f32)) == maxInt(i32));
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expect(ilogb32(-math.inf(f32)) == maxInt(i32));
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expect(ilogb32(0.0) == minInt(i32));
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expect(ilogb32(math.nan(f32)) == maxInt(i32));
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}
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test "math.ilogb64.special" {
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expect(ilogb64(math.inf(f64)) == maxInt(i32));
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expect(ilogb64(-math.inf(f64)) == maxInt(i32));
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expect(ilogb64(0.0) == minInt(i32));
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expect(ilogb64(math.nan(f64)) == maxInt(i32));
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}
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