Merge pull request 'libzigc: cbrt, cbrtf' (#31078) from jeffective/zig:jeff/libzigc-cbrt into master

Reviewed-on: https://codeberg.org/ziglang/zig/pulls/31078
Reviewed-by: Andrew Kelley <andrew@ziglang.org>

lib/c/math.zig

@@ -39,6 +39,8 @@ 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 });
+        @export(&cbrtf, .{ .name = "cbrtf", .linkage = common.linkage, .visibility = common.visibility });
     }
 
     if (builtin.target.isMuslLibC()) {
@@ -106,3 +108,11 @@ 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);
+}
+
+fn cbrtf(x: f32) callconv(.c) f32 {
+    return math.cbrt(x);
+}

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;
-}

lib/libc/musl/src/math/cbrtf.c

@@ -1,66 +0,0 @@
-/* origin: FreeBSD /usr/src/lib/msun/src/s_cbrtf.c */
-/*
- * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
- * Debugged and optimized by Bruce D. Evans.
- */
-/*
- * ====================================================
- * 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.
- * ====================================================
- */
-/* cbrtf(x)
- * Return cube root of x
- */
-
-#include <math.h>
-#include <stdint.h>
-
-static const unsigned
-B1 = 709958130, /* B1 = (127-127.0/3-0.03306235651)*2**23 */
-B2 = 642849266; /* B2 = (127-127.0/3-24/3-0.03306235651)*2**23 */
-
-float cbrtf(float x)
-{
-	double_t r,T;
-	union {float f; uint32_t i;} u = {x};
-	uint32_t hx = u.i & 0x7fffffff;
-
-	if (hx >= 0x7f800000)  /* cbrt(NaN,INF) is itself */
-		return x + x;
-
-	/* rough cbrt to 5 bits */
-	if (hx < 0x00800000) {  /* zero or subnormal? */
-		if (hx == 0)
-			return x;  /* cbrt(+-0) is itself */
-		u.f = x*0x1p24f;
-		hx = u.i & 0x7fffffff;
-		hx = hx/3 + B2;
-	} else
-		hx = hx/3 + B1;
-	u.i &= 0x80000000;
-	u.i |= hx;
-
-	/*
-	 * First step Newton iteration (solving t*t-x/t == 0) to 16 bits.  In
-	 * double precision so that its terms can be arranged for efficiency
-	 * without causing overflow or underflow.
-	 */
-	T = u.f;
-	r = T*T*T;
-	T = T*((double_t)x+x+r)/(x+r+r);
-
-	/*
-	 * Second step Newton iteration to 47 bits.  In double precision for
-	 * efficiency and accuracy.
-	 */
-	r = T*T*T;
-	T = T*((double_t)x+x+r)/(x+r+r);
-
-	/* rounding to 24 bits is perfect in round-to-nearest mode */
-	return T;
-}

src/libs/musl.zig

@@ -837,8 +837,6 @@ 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",
     "musl/src/math/__cosdf.c",

src/libs/wasi_libc.zig

@@ -701,8 +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",
     "musl/src/math/__cosdf.c",