log2l lacks precision on musl libc 1.2.2/arm64, musl libc 1.2.2/s390x. This patch adds a configure test, that enables a gnulib workaround.
2021-01-31 Bruno Haible <br...@clisp.org> log2l: Work around musl libc bugs. * doc/posix-functions/log2l.texi: Document musl libc bugs. * m4/log2l.m4 (gl_FUNC_LOG2L_WORKS): Add more tests. Update cross compilation guess. diff --git a/doc/posix-functions/log2l.texi b/doc/posix-functions/log2l.texi index 24e367c..563a67e 100644 --- a/doc/posix-functions/log2l.texi +++ b/doc/posix-functions/log2l.texi @@ -14,6 +14,13 @@ FreeBSD 6.0, NetBSD 9.0, OpenBSD 3.8, Minix 3.1.8, AIX 5.1, HP-UX 11, older IRIX @item This function is not declared on some platforms: IRIX 6.5. +@item +This function produces results which are accurate to only 16 digits on some +platforms: +musl libc 1.2.2/arm64, musl libc 1.2.2/s390x. +@item +This function returns Infinity for some large finite arguments on some platforms: +musl libc 1.2.2/arm64, musl libc 1.2.2/s390x. @end itemize Portability problems not fixed by Gnulib: diff --git a/m4/log2l.m4 b/m4/log2l.m4 index 4776543..cd8e984 100644 --- a/m4/log2l.m4 +++ b/m4/log2l.m4 @@ -1,4 +1,4 @@ -# log2l.m4 serial 2 +# log2l.m4 serial 3 dnl Copyright (C) 2010-2021 Free Software Foundation, Inc. dnl This file is free software; the Free Software Foundation dnl gives unlimited permission to copy and/or distribute it, @@ -69,6 +69,7 @@ AC_DEFUN([gl_FUNC_LOG2L], dnl Test whether log2l() works. dnl On OSF/1 5.1, log2l(-0.0) is NaN. +dnl On musl 1.2.2/{arm64,s390x}, the result is accurate to only 16 digits. AC_DEFUN([gl_FUNC_LOG2L_WORKS], [ AC_REQUIRE([AC_PROG_CC]) @@ -77,7 +78,40 @@ AC_DEFUN([gl_FUNC_LOG2L_WORKS], [ AC_RUN_IFELSE( [AC_LANG_SOURCE([[ +#ifndef __NO_MATH_INLINES +# define __NO_MATH_INLINES 1 /* for glibc */ +#endif +#include <float.h> #include <math.h> +/* Override the values of <float.h>, like done in float.in.h. */ +#if defined __i386__ && (defined __BEOS__ || defined __OpenBSD__) +# undef LDBL_MANT_DIG +# define LDBL_MANT_DIG 64 +# undef LDBL_MIN_EXP +# define LDBL_MIN_EXP (-16381) +# undef LDBL_MAX_EXP +# define LDBL_MAX_EXP 16384 +#endif +#if defined __i386__ && (defined __FreeBSD__ || defined __DragonFly__) +# undef LDBL_MANT_DIG +# define LDBL_MANT_DIG 64 +# undef LDBL_MIN_EXP +# define LDBL_MIN_EXP (-16381) +# undef LDBL_MAX_EXP +# define LDBL_MAX_EXP 16384 +#endif +#if (defined _ARCH_PPC || defined _POWER) && defined _AIX && (LDBL_MANT_DIG == 106) && defined __GNUC__ +# undef LDBL_MIN_EXP +# define LDBL_MIN_EXP DBL_MIN_EXP +#endif +#if defined __sgi && (LDBL_MANT_DIG >= 106) +# undef LDBL_MANT_DIG +# define LDBL_MANT_DIG 106 +# if defined __GNUC__ +# undef LDBL_MIN_EXP +# define LDBL_MIN_EXP DBL_MIN_EXP +# endif +#endif #ifndef log2l /* for AIX */ extern #ifdef __cplusplus @@ -85,25 +119,59 @@ extern #endif long double log2l (long double); #endif -volatile long double x; -volatile long double y; -int main () +static long double dummy (long double x) { return 0; } +volatile long double gx; +volatile long double gy; +int main (int argc, char *argv[]) { + long double (* volatile my_log2l) (long double) = argc ? log2l : dummy; + int result = 0; /* This test fails on OSF/1 5.1. */ - x = -0.0L; - y = log2l (x); - if (!(y + y == y)) - return 1; - return 0; + { + gx = -0.0L; + gy = my_log2l (gx); + if (!(gy + gy == gy)) + result |= 1; + } + /* This test fails on musl 1.2.2/arm64, musl 1.2.2/s390x. */ + { + const long double TWO_LDBL_MANT_DIG = /* 2^LDBL_MANT_DIG */ + (long double) (1U << ((LDBL_MANT_DIG - 1) / 5)) + * (long double) (1U << ((LDBL_MANT_DIG - 1 + 1) / 5)) + * (long double) (1U << ((LDBL_MANT_DIG - 1 + 2) / 5)) + * (long double) (1U << ((LDBL_MANT_DIG - 1 + 3) / 5)) + * (long double) (1U << ((LDBL_MANT_DIG - 1 + 4) / 5)); + long double x = 11.358L; + long double y = my_log2l (x); + long double z = my_log2l (1.0L / x); + long double err = (y + z) * TWO_LDBL_MANT_DIG; + if (!(err >= -10000.0L && err <= 10000.0L)) + result |= 2; + } + /* This test fails on musl 1.2.2/arm64, musl 1.2.2/s390x. */ + if (DBL_MAX_EXP < LDBL_MAX_EXP) + { + long double x = ldexpl (1.0L, DBL_MAX_EXP); /* finite! */ + long double y = my_log2l (x); + if (y > 0 && y + y == y) /* infinite? */ + result |= 4; + } + return result; } ]])], [gl_cv_func_log2l_works=yes], [gl_cv_func_log2l_works=no], [case "$host_os" in - osf*) gl_cv_func_log2l_works="guessing no" ;; - # Guess yes on native Windows. - mingw*) gl_cv_func_log2l_works="guessing yes" ;; - *) gl_cv_func_log2l_works="guessing yes" ;; + # Guess yes on glibc systems. + *-gnu* | gnu*) gl_cv_func_log2l_works="guessing yes" ;; + # Guess no on musl systems. + *-musl*) gl_cv_func_log2l_works="guessing no" ;; + # Guess no on OSF/1. + osf*) gl_cv_func_log2l_works="guessing no" ;; + # Guess yes on native Windows. + mingw*) gl_cv_func_log2l_works="guessing yes" ;; + # If we don't know, obey --enable-cross-guesses. + *) gl_cv_func_log2l_works="$gl_cross_guess_normal" ;; esac ]) ])