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d29871977f
We already have a LICENSE file that covers the Zig Standard Library. We no longer need to remind everyone that the license is MIT in every single file. Previously this was introduced to clarify the situation for a fork of Zig that made Zig's LICENSE file harder to find, and replaced it with their own license that required annual payments to their company. However that fork now appears to be dead. So there is no need to reinforce the copyright notice in every single file.
138 lines
3.3 KiB
Zig
138 lines
3.3 KiB
Zig
// 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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try expect(ilogb(@as(f32, 0.2)) == ilogb32(0.2));
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try expect(ilogb(@as(f64, 0.2)) == ilogb64(0.2));
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}
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test "math.ilogb32" {
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try expect(ilogb32(0.0) == fp_ilogb0);
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try expect(ilogb32(0.5) == -1);
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try expect(ilogb32(0.8923) == -1);
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try expect(ilogb32(10.0) == 3);
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try expect(ilogb32(-123984) == 16);
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try expect(ilogb32(2398.23) == 11);
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}
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test "math.ilogb64" {
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try expect(ilogb64(0.0) == fp_ilogb0);
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try expect(ilogb64(0.5) == -1);
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try expect(ilogb64(0.8923) == -1);
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try expect(ilogb64(10.0) == 3);
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try expect(ilogb64(-123984) == 16);
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try expect(ilogb64(2398.23) == 11);
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}
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test "math.ilogb32.special" {
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try expect(ilogb32(math.inf(f32)) == maxInt(i32));
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try expect(ilogb32(-math.inf(f32)) == maxInt(i32));
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try expect(ilogb32(0.0) == minInt(i32));
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try expect(ilogb32(math.nan(f32)) == maxInt(i32));
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}
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test "math.ilogb64.special" {
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try expect(ilogb64(math.inf(f64)) == maxInt(i32));
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try expect(ilogb64(-math.inf(f64)) == maxInt(i32));
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try expect(ilogb64(0.0) == minInt(i32));
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try expect(ilogb64(math.nan(f64)) == maxInt(i32));
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}
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