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-rw-r--r--lib/std/math/log10.zig218
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diff --git a/lib/std/math/log10.zig b/lib/std/math/log10.zig
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+// 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/log10f.c
+// https://git.musl-libc.org/cgit/musl/tree/src/math/log10.c
+
+const std = @import("../std.zig");
+const math = std.math;
+const testing = std.testing;
+const builtin = @import("builtin");
+const TypeId = builtin.TypeId;
+const maxInt = std.math.maxInt;
+
+/// Returns the base-10 logarithm of x.
+///
+/// Special Cases:
+/// - log10(+inf) = +inf
+/// - log10(0) = -inf
+/// - log10(x) = nan if x < 0
+/// - log10(nan) = nan
+pub fn log10(x: var) @typeOf(x) {
+ const T = @typeOf(x);
+ switch (@typeId(T)) {
+ TypeId.ComptimeFloat => {
+ return @typeOf(1.0)(log10_64(x));
+ },
+ TypeId.Float => {
+ return switch (T) {
+ f32 => log10_32(x),
+ f64 => log10_64(x),
+ else => @compileError("log10 not implemented for " ++ @typeName(T)),
+ };
+ },
+ TypeId.ComptimeInt => {
+ return @typeOf(1)(math.floor(log10_64(f64(x))));
+ },
+ TypeId.Int => {
+ return @floatToInt(T, math.floor(log10_64(@intToFloat(f64, x))));
+ },
+ else => @compileError("log10 not implemented for " ++ @typeName(T)),
+ }
+}
+
+pub fn log10_32(x_: f32) f32 {
+ const ivln10hi: f32 = 4.3432617188e-01;
+ const ivln10lo: f32 = -3.1689971365e-05;
+ const log10_2hi: f32 = 3.0102920532e-01;
+ const log10_2lo: f32 = 7.9034151668e-07;
+ const Lg1: f32 = 0xaaaaaa.0p-24;
+ const Lg2: f32 = 0xccce13.0p-25;
+ const Lg3: f32 = 0x91e9ee.0p-25;
+ const Lg4: f32 = 0xf89e26.0p-26;
+
+ var x = x_;
+ var u = @bitCast(u32, x);
+ var ix = u;
+ var k: i32 = 0;
+
+ // x < 2^(-126)
+ if (ix < 0x00800000 or ix >> 31 != 0) {
+ // log(+-0) = -inf
+ if (ix << 1 == 0) {
+ return -math.inf(f32);
+ }
+ // log(-#) = nan
+ if (ix >> 31 != 0) {
+ return math.nan(f32);
+ }
+
+ k -= 25;
+ x *= 0x1.0p25;
+ ix = @bitCast(u32, x);
+ } else if (ix >= 0x7F800000) {
+ return x;
+ } else if (ix == 0x3F800000) {
+ return 0;
+ }
+
+ // x into [sqrt(2) / 2, sqrt(2)]
+ ix += 0x3F800000 - 0x3F3504F3;
+ k += @intCast(i32, ix >> 23) - 0x7F;
+ ix = (ix & 0x007FFFFF) + 0x3F3504F3;
+ x = @bitCast(f32, ix);
+
+ const f = x - 1.0;
+ const s = f / (2.0 + f);
+ const z = s * s;
+ const w = z * z;
+ const t1 = w * (Lg2 + w * Lg4);
+ const t2 = z * (Lg1 + w * Lg3);
+ const R = t2 + t1;
+ const hfsq = 0.5 * f * f;
+
+ var hi = f - hfsq;
+ u = @bitCast(u32, hi);
+ u &= 0xFFFFF000;
+ hi = @bitCast(f32, u);
+ const lo = f - hi - hfsq + s * (hfsq + R);
+ const dk = @intToFloat(f32, k);
+
+ return dk * log10_2lo + (lo + hi) * ivln10lo + lo * ivln10hi + hi * ivln10hi + dk * log10_2hi;
+}
+
+pub fn log10_64(x_: f64) f64 {
+ const ivln10hi: f64 = 4.34294481878168880939e-01;
+ const ivln10lo: f64 = 2.50829467116452752298e-11;
+ const log10_2hi: f64 = 3.01029995663611771306e-01;
+ const log10_2lo: f64 = 3.69423907715893078616e-13;
+ const Lg1: f64 = 6.666666666666735130e-01;
+ const Lg2: f64 = 3.999999999940941908e-01;
+ const Lg3: f64 = 2.857142874366239149e-01;
+ const Lg4: f64 = 2.222219843214978396e-01;
+ const Lg5: f64 = 1.818357216161805012e-01;
+ const Lg6: f64 = 1.531383769920937332e-01;
+ const Lg7: f64 = 1.479819860511658591e-01;
+
+ var x = x_;
+ var ix = @bitCast(u64, x);
+ var hx = @intCast(u32, ix >> 32);
+ var k: i32 = 0;
+
+ if (hx < 0x00100000 or hx >> 31 != 0) {
+ // log(+-0) = -inf
+ if (ix << 1 == 0) {
+ return -math.inf(f32);
+ }
+ // log(-#) = nan
+ if (hx >> 31 != 0) {
+ return math.nan(f32);
+ }
+
+ // subnormal, scale x
+ k -= 54;
+ x *= 0x1.0p54;
+ hx = @intCast(u32, @bitCast(u64, x) >> 32);
+ } else if (hx >= 0x7FF00000) {
+ return x;
+ } else if (hx == 0x3FF00000 and ix << 32 == 0) {
+ return 0;
+ }
+
+ // x into [sqrt(2) / 2, sqrt(2)]
+ hx += 0x3FF00000 - 0x3FE6A09E;
+ k += @intCast(i32, hx >> 20) - 0x3FF;
+ hx = (hx & 0x000FFFFF) + 0x3FE6A09E;
+ ix = (u64(hx) << 32) | (ix & 0xFFFFFFFF);
+ x = @bitCast(f64, ix);
+
+ const f = x - 1.0;
+ const hfsq = 0.5 * f * f;
+ const s = f / (2.0 + f);
+ const z = s * s;
+ const w = z * z;
+ const t1 = w * (Lg2 + w * (Lg4 + w * Lg6));
+ const t2 = z * (Lg1 + w * (Lg3 + w * (Lg5 + w * Lg7)));
+ const R = t2 + t1;
+
+ // hi + lo = f - hfsq + s * (hfsq + R) ~ log(1 + f)
+ var hi = f - hfsq;
+ var hii = @bitCast(u64, hi);
+ hii &= u64(maxInt(u64)) << 32;
+ hi = @bitCast(f64, hii);
+ const lo = f - hi - hfsq + s * (hfsq + R);
+
+ // val_hi + val_lo ~ log10(1 + f) + k * log10(2)
+ var val_hi = hi * ivln10hi;
+ const dk = @intToFloat(f64, k);
+ const y = dk * log10_2hi;
+ var val_lo = dk * log10_2lo + (lo + hi) * ivln10lo + lo * ivln10hi;
+
+ // Extra precision multiplication
+ const ww = y + val_hi;
+ val_lo += (y - ww) + val_hi;
+ val_hi = ww;
+
+ return val_lo + val_hi;
+}
+
+test "math.log10" {
+ testing.expect(log10(f32(0.2)) == log10_32(0.2));
+ testing.expect(log10(f64(0.2)) == log10_64(0.2));
+}
+
+test "math.log10_32" {
+ const epsilon = 0.000001;
+
+ testing.expect(math.approxEq(f32, log10_32(0.2), -0.698970, epsilon));
+ testing.expect(math.approxEq(f32, log10_32(0.8923), -0.049489, epsilon));
+ testing.expect(math.approxEq(f32, log10_32(1.5), 0.176091, epsilon));
+ testing.expect(math.approxEq(f32, log10_32(37.45), 1.573452, epsilon));
+ testing.expect(math.approxEq(f32, log10_32(89.123), 1.94999, epsilon));
+ testing.expect(math.approxEq(f32, log10_32(123123.234375), 5.09034, epsilon));
+}
+
+test "math.log10_64" {
+ const epsilon = 0.000001;
+
+ testing.expect(math.approxEq(f64, log10_64(0.2), -0.698970, epsilon));
+ testing.expect(math.approxEq(f64, log10_64(0.8923), -0.049489, epsilon));
+ testing.expect(math.approxEq(f64, log10_64(1.5), 0.176091, epsilon));
+ testing.expect(math.approxEq(f64, log10_64(37.45), 1.573452, epsilon));
+ testing.expect(math.approxEq(f64, log10_64(89.123), 1.94999, epsilon));
+ testing.expect(math.approxEq(f64, log10_64(123123.234375), 5.09034, epsilon));
+}
+
+test "math.log10_32.special" {
+ testing.expect(math.isPositiveInf(log10_32(math.inf(f32))));
+ testing.expect(math.isNegativeInf(log10_32(0.0)));
+ testing.expect(math.isNan(log10_32(-1.0)));
+ testing.expect(math.isNan(log10_32(math.nan(f32))));
+}
+
+test "math.log10_64.special" {
+ testing.expect(math.isPositiveInf(log10_64(math.inf(f64))));
+ testing.expect(math.isNegativeInf(log10_64(0.0)));
+ testing.expect(math.isNan(log10_64(-1.0)));
+ testing.expect(math.isNan(log10_64(math.nan(f64))));
+}
generated by cgit v1.2.3 (git 2.39.1) at 2025-12-27 19:49:41 +0000