commit 0aae9768aab8e1b534eb9a7682ad36ab4ef0487d (tree)
parent 3abc96a601d2349cc1743774f0cebb2eb0ea0c61
Author: Jeff Anderson <kj4tmp@gmail.com>
Date: Sat, 31 Jan 2026 21:54:25 -0800
libzigc: cbrt
Diffstat:
4 files changed, 5 insertions(+), 105 deletions(-)
diff --git a/lib/c/math.zig b/lib/c/math.zig
@@ -39,6 +39,7 @@ comptime {
@export(&atanf, .{ .name = "atanf", .linkage = common.linkage, .visibility = common.visibility });
@export(&atan, .{ .name = "atan", .linkage = common.linkage, .visibility = common.visibility });
@export(&atanl, .{ .name = "atanl", .linkage = common.linkage, .visibility = common.visibility });
+ @export(&cbrt, .{ .name = "cbrt", .linkage = common.linkage, .visibility = common.visibility });
}
if (builtin.target.isMuslLibC()) {
@@ -106,3 +107,7 @@ fn copysign(x: f64, y: f64) callconv(.c) f64 {
fn copysignl(x: c_longdouble, y: c_longdouble) callconv(.c) c_longdouble {
return math.copysign(x, y);
}
+
+fn cbrt(x: f64) callconv(.c) f64 {
+ return math.cbrt(x);
+}
diff --git a/lib/libc/musl/src/math/cbrt.c b/lib/libc/musl/src/math/cbrt.c
@@ -1,103 +0,0 @@
-/* origin: FreeBSD /usr/src/lib/msun/src/s_cbrt.c */
-/*
- * ====================================================
- * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
- *
- * Developed at SunPro, a Sun Microsystems, Inc. business.
- * Permission to use, copy, modify, and distribute this
- * software is freely granted, provided that this notice
- * is preserved.
- * ====================================================
- *
- * Optimized by Bruce D. Evans.
- */
-/* cbrt(x)
- * Return cube root of x
- */
-
-#include <math.h>
-#include <stdint.h>
-
-static const uint32_t
-B1 = 715094163, /* B1 = (1023-1023/3-0.03306235651)*2**20 */
-B2 = 696219795; /* B2 = (1023-1023/3-54/3-0.03306235651)*2**20 */
-
-/* |1/cbrt(x) - p(x)| < 2**-23.5 (~[-7.93e-8, 7.929e-8]). */
-static const double
-P0 = 1.87595182427177009643, /* 0x3ffe03e6, 0x0f61e692 */
-P1 = -1.88497979543377169875, /* 0xbffe28e0, 0x92f02420 */
-P2 = 1.621429720105354466140, /* 0x3ff9f160, 0x4a49d6c2 */
-P3 = -0.758397934778766047437, /* 0xbfe844cb, 0xbee751d9 */
-P4 = 0.145996192886612446982; /* 0x3fc2b000, 0xd4e4edd7 */
-
-double cbrt(double x)
-{
- union {double f; uint64_t i;} u = {x};
- double_t r,s,t,w;
- uint32_t hx = u.i>>32 & 0x7fffffff;
-
- if (hx >= 0x7ff00000) /* cbrt(NaN,INF) is itself */
- return x+x;
-
- /*
- * Rough cbrt to 5 bits:
- * cbrt(2**e*(1+m) ~= 2**(e/3)*(1+(e%3+m)/3)
- * where e is integral and >= 0, m is real and in [0, 1), and "/" and
- * "%" are integer division and modulus with rounding towards minus
- * infinity. The RHS is always >= the LHS and has a maximum relative
- * error of about 1 in 16. Adding a bias of -0.03306235651 to the
- * (e%3+m)/3 term reduces the error to about 1 in 32. With the IEEE
- * floating point representation, for finite positive normal values,
- * ordinary integer divison of the value in bits magically gives
- * almost exactly the RHS of the above provided we first subtract the
- * exponent bias (1023 for doubles) and later add it back. We do the
- * subtraction virtually to keep e >= 0 so that ordinary integer
- * division rounds towards minus infinity; this is also efficient.
- */
- if (hx < 0x00100000) { /* zero or subnormal? */
- u.f = x*0x1p54;
- hx = u.i>>32 & 0x7fffffff;
- if (hx == 0)
- return x; /* cbrt(0) is itself */
- hx = hx/3 + B2;
- } else
- hx = hx/3 + B1;
- u.i &= 1ULL<<63;
- u.i |= (uint64_t)hx << 32;
- t = u.f;
-
- /*
- * New cbrt to 23 bits:
- * cbrt(x) = t*cbrt(x/t**3) ~= t*P(t**3/x)
- * where P(r) is a polynomial of degree 4 that approximates 1/cbrt(r)
- * to within 2**-23.5 when |r - 1| < 1/10. The rough approximation
- * has produced t such than |t/cbrt(x) - 1| ~< 1/32, and cubing this
- * gives us bounds for r = t**3/x.
- *
- * Try to optimize for parallel evaluation as in __tanf.c.
- */
- r = (t*t)*(t/x);
- t = t*((P0+r*(P1+r*P2))+((r*r)*r)*(P3+r*P4));
-
- /*
- * Round t away from zero to 23 bits (sloppily except for ensuring that
- * the result is larger in magnitude than cbrt(x) but not much more than
- * 2 23-bit ulps larger). With rounding towards zero, the error bound
- * would be ~5/6 instead of ~4/6. With a maximum error of 2 23-bit ulps
- * in the rounded t, the infinite-precision error in the Newton
- * approximation barely affects third digit in the final error
- * 0.667; the error in the rounded t can be up to about 3 23-bit ulps
- * before the final error is larger than 0.667 ulps.
- */
- u.f = t;
- u.i = (u.i + 0x80000000) & 0xffffffffc0000000ULL;
- t = u.f;
-
- /* one step Newton iteration to 53 bits with error < 0.667 ulps */
- s = t*t; /* t*t is exact */
- r = x/s; /* error <= 0.5 ulps; |r| < |t| */
- w = t+t; /* t+t is exact */
- r = (r-t)/(w+r); /* r-t is exact; w+r ~= 3*t */
- t = t+t*r; /* error <= 0.5 + 0.5/3 + epsilon */
- return t;
-}
diff --git a/src/libs/musl.zig b/src/libs/musl.zig
@@ -839,7 +839,6 @@ const src_files = [_][]const u8{
"musl/src/math/atanh.c",
"musl/src/math/atanhf.c",
"musl/src/math/atanhl.c",
- "musl/src/math/cbrt.c",
"musl/src/math/cbrtf.c",
"musl/src/math/cbrtl.c",
"musl/src/math/__cos.c",
diff --git a/src/libs/wasi_libc.zig b/src/libs/wasi_libc.zig
@@ -701,7 +701,6 @@ const libc_top_half_src_files = [_][]const u8{
"musl/src/math/atanh.c",
"musl/src/math/atanhf.c",
"musl/src/math/atanhl.c",
- "musl/src/math/cbrt.c",
"musl/src/math/cbrtf.c",
"musl/src/math/cbrtl.c",
"musl/src/math/__cos.c",
