bug#25785: scm_c_make_polar broken on APPLE

[Matt Wette]

numbers.c:scm_c_make_polar in guile-2.1.7 breaks on APPLE (macOS 10.12).

Reason: APPLE does not have sincos(), and gcc will optimize sin/cos to use cexp(), and cexp() does not preserve sign of zero.

Patch includes (and attached) for guile-2.1.7.  This uses macOS __sincos().

Example:

In scm_c_make_polar, “gcc -O2”  turns sin(), cos() into cexp(), since cexp(i*x) = cos(x) + i*sin(x):

gcc -O0 =>

LM4339:

movq -32(%rbp), %rax

movd %rax, %xmm0

call _sin

movd %xmm0, %rax

movq %rax, -8(%rbp)

LM4340:

movq -32(%rbp), %rax

movd %rax, %xmm0

call _cos

movd %xmm0, %rax

movq %rax, -16(%rbp)

gcc -O2 =>

pxor %xmm0, %xmm0

LVL2703:

call _cexp

I wrote a little C program to show that cexp() does not preserve the zero-signed-ness:

 cos,sin: +1.000000 -0.000000

__sincos: +1.000000 -0.000000

    cexp: +1.000000 +0.000000

The scm_c_make_polar will use sincos() if available, but macOS does not have sincos(), it has __sincos().

#include <stdio.h>

#include <stdint.h>

#include <math.h>

#include <complex.h>

extern double z, p, n;

int main() {

  double complex c;

  double d, sine, cosine;

  d = z*n;

  printf(" cos,sin: %+f %+f\n", cos(d), sin(d));

  __sincos(d, &sine, &cosine);

  printf("__sincos: %+f %+f\n", cosine, sine);

  c = cexp(CMPLX(0.0, d));

  printf("    cexp: %+f %+f\n", creal(c), cimag(c));

}

double z = 0.0, p = +1.0, n = -1.0;

--- configure.ac.orig 2017-02-18 08:35:06.000000000 -0800

+++ configure.ac 2017-02-18 08:35:26.000000000 -0800

@@ -1152,8 +1152,9 @@

 #   asinh, acosh, atanh, trunc - C99 standard, generally not available on

 #                                older systems

 #   sincos - GLIBC extension

+#   __sincos - APPLE extension

 #

-AC_CHECK_FUNCS(asinh acosh atanh copysign finite sincos trunc)

+AC_CHECK_FUNCS(asinh acosh atanh copysign finite sincos __sincos trunc)

 

 # C99 specifies isinf and isnan as macros.

 # HP-UX provides only macros, no functions.

--- libguile/numbers.c.patch.labs 2017-02-18 08:31:21.000000000 -0800

+++ libguile/numbers.c 2017-02-18 08:34:18.000000000 -0800

@@ -9109,6 +9109,8 @@

      details.  */

 #if (defined HAVE_SINCOS) && (defined __GLIBC__) && (defined _GNU_SOURCE)

   sincos (ang, &s, &c);

+#elif (defined HAVE___SINCOS)

+  __sincos (ang, &s, &c);

 #else

   s = sin (ang);

   c = cos (ang);

sincos.patch
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