Commit 74f87fd1 authored by Paul Eggert's avatar Paul Eggert

logb now works correctly on large integers

* admin/merge-gnulib (GNULIB_MODULES): Add count-leading-zeros.
* etc/NEWS: Document the change.
* lib/count-leading-zeros.c, lib/count-leading-zeros.h:
* m4/count-leading-zeros.m4: New files, copied from Gnulib.
* lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate.
* src/floatfns.c: Include count-leading-zeros.h.
(Flogb): Do not convert fixnum to float before taking the log,
as the rounding error can cause the answer to be off by 1.
* src/lisp.h (EMACS_UINT_WIDTH): New constant.
* test/src/floatfns-tests.el (logb-extreme-fixnum): New test.
parent f1fe3fcf
......@@ -27,7 +27,8 @@ GNULIB_URL=git://git.savannah.gnu.org/gnulib.git
GNULIB_MODULES='
alloca-opt binary-io byteswap c-ctype c-strcase
careadlinkat close-stream count-one-bits count-trailing-zeros
careadlinkat close-stream
count-leading-zeros count-one-bits count-trailing-zeros
crypto/md5 crypto/sha1 crypto/sha256 crypto/sha512
dtoastr dtotimespec dup2 environ execinfo faccessat
fcntl fcntl-h fdatasync fdopendir
......
......@@ -903,9 +903,9 @@ compares their numerical values. According to this predicate,
"foo2.png" is smaller than "foo12.png".
---
** Numeric comparisons no longer return incorrect answers due to
internal rounding errors. For example, (< most-positive-fixnum (+ 1.0
most-positive-fixnum)) now correctly returns t on 64-bit hosts.
** Numeric comparisons and 'logb' no longer return incorrect answers
due to internal rounding errors. For example, (< most-positive-fixnum
(+ 1.0 most-positive-fixnum)) now correctly returns t on 64-bit hosts.
+++
** The new function 'char-from-name' converts a Unicode name string
......
#include <config.h>
#define COUNT_LEADING_ZEROS_INLINE _GL_EXTERN_INLINE
#include "count-leading-zeros.h"
/* count-leading-zeros.h -- counts the number of leading 0 bits in a word.
Copyright (C) 2012-2017 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
/* Written by Eric Blake. */
#ifndef COUNT_LEADING_ZEROS_H
#define COUNT_LEADING_ZEROS_H 1
#include <limits.h>
#include <stdlib.h>
#ifndef _GL_INLINE_HEADER_BEGIN
#error "Please include config.h first."
#endif
_GL_INLINE_HEADER_BEGIN
#ifndef COUNT_LEADING_ZEROS_INLINE
# define COUNT_LEADING_ZEROS_INLINE _GL_INLINE
#endif
/* Assuming the GCC builtin is BUILTIN and the MSC builtin is MSC_BUILTIN,
expand to code that computes the number of leading zeros of the local
variable 'x' of type TYPE (an unsigned integer type) and return it
from the current function. */
#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
# define COUNT_LEADING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
return x ? BUILTIN (x) : CHAR_BIT * sizeof x;
#elif _MSC_VER
# pragma intrinsic _BitScanReverse
# pragma intrinsic _BitScanReverse64
# define COUNT_LEADING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
do \
{ \
unsigned long result; \
return MSC_BUILTIN (&result, x) ? result : CHAR_BIT * sizeof x; \
} \
while (0)
#else
# define COUNT_LEADING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
do \
{ \
int count; \
unsigned int leading_32; \
if (! x) \
return CHAR_BIT * sizeof x; \
for (count = 0; \
(leading_32 = ((x >> (sizeof (TYPE) * CHAR_BIT - 32)) \
& 0xffffffffU), \
count < CHAR_BIT * sizeof x - 32 && !leading_32); \
count += 32) \
x = x << 31 << 1; \
return count + count_leading_zeros_32 (leading_32); \
} \
while (0)
/* Compute and return the number of leading zeros in X,
where 0 < X < 2**32. */
COUNT_LEADING_ZEROS_INLINE int
count_leading_zeros_32 (unsigned int x)
{
/* http://graphics.stanford.edu/~seander/bithacks.html */
static const char de_Bruijn_lookup[32] = {
31, 22, 30, 21, 18, 10, 29, 2, 20, 17, 15, 13, 9, 6, 28, 1,
23, 19, 11, 3, 16, 14, 7, 24, 12, 4, 8, 25, 5, 26, 27, 0
};
x |= x >> 1;
x |= x >> 2;
x |= x >> 4;
x |= x >> 8;
x |= x >> 16;
return de_Bruijn_lookup[((x * 0x07c4acddU) & 0xffffffffU) >> 27];
}
#endif
/* Compute and return the number of leading zeros in X. */
COUNT_LEADING_ZEROS_INLINE int
count_leading_zeros (unsigned int x)
{
COUNT_LEADING_ZEROS (__builtin_clz, _BitScanReverse, unsigned int);
}
/* Compute and return the number of leading zeros in X. */
COUNT_LEADING_ZEROS_INLINE int
count_leading_zeros_l (unsigned long int x)
{
COUNT_LEADING_ZEROS (__builtin_clzl, _BitScanReverse, unsigned long int);
}
#if HAVE_UNSIGNED_LONG_LONG_INT
/* Compute and return the number of leading zeros in X. */
COUNT_LEADING_ZEROS_INLINE int
count_leading_zeros_ll (unsigned long long int x)
{
COUNT_LEADING_ZEROS (__builtin_clzll, _BitScanReverse64,
unsigned long long int);
}
#endif
_GL_INLINE_HEADER_END
#endif /* COUNT_LEADING_ZEROS_H */
......@@ -21,7 +21,7 @@
# the same distribution terms as the rest of that program.
#
# Generated by gnulib-tool.
# Reproduce by: gnulib-tool --import --lib=libgnu --source-base=lib --m4-base=m4 --doc-base=doc --tests-base=tests --aux-dir=build-aux --avoid=close --avoid=dup --avoid=fchdir --avoid=fstat --avoid=malloc-posix --avoid=msvc-inval --avoid=msvc-nothrow --avoid=open --avoid=openat-die --avoid=opendir --avoid=raise --avoid=save-cwd --avoid=select --avoid=setenv --avoid=sigprocmask --avoid=stdarg --avoid=stdbool --avoid=threadlib --avoid=unsetenv --makefile-name=gnulib.mk --conditional-dependencies --no-libtool --macro-prefix=gl --no-vc-files alloca-opt binary-io byteswap c-ctype c-strcase careadlinkat close-stream count-one-bits count-trailing-zeros crypto/md5 crypto/sha1 crypto/sha256 crypto/sha512 dtoastr dtotimespec dup2 environ execinfo faccessat fcntl fcntl-h fdatasync fdopendir filemode filevercmp flexmember fstatat fsync getloadavg getopt-gnu gettime gettimeofday gitlog-to-changelog ignore-value intprops largefile lstat manywarnings memrchr mkostemp mktime pipe2 pselect pthread_sigmask putenv qcopy-acl readlink readlinkat sig2str socklen stat-time std-gnu11 stdalign stddef stdio stpcpy strftime strtoimax strtoumax symlink sys_stat sys_time time time_r time_rz timegm timer-time timespec-add timespec-sub unsetenv update-copyright utimens vla warnings
# Reproduce by: gnulib-tool --import --lib=libgnu --source-base=lib --m4-base=m4 --doc-base=doc --tests-base=tests --aux-dir=build-aux --avoid=close --avoid=dup --avoid=fchdir --avoid=fstat --avoid=malloc-posix --avoid=msvc-inval --avoid=msvc-nothrow --avoid=open --avoid=openat-die --avoid=opendir --avoid=raise --avoid=save-cwd --avoid=select --avoid=setenv --avoid=sigprocmask --avoid=stdarg --avoid=stdbool --avoid=threadlib --avoid=unsetenv --makefile-name=gnulib.mk --conditional-dependencies --no-libtool --macro-prefix=gl --no-vc-files alloca-opt binary-io byteswap c-ctype c-strcase careadlinkat close-stream count-leading-zeros count-one-bits count-trailing-zeros crypto/md5 crypto/sha1 crypto/sha256 crypto/sha512 dtoastr dtotimespec dup2 environ execinfo faccessat fcntl fcntl-h fdatasync fdopendir filemode filevercmp flexmember fstatat fsync getloadavg getopt-gnu gettime gettimeofday gitlog-to-changelog ignore-value intprops largefile lstat manywarnings memrchr mkostemp mktime pipe2 pselect pthread_sigmask putenv qcopy-acl readlink readlinkat sig2str socklen stat-time std-gnu11 stdalign stddef stdio stpcpy strftime strtoimax strtoumax symlink sys_stat sys_time time time_r time_rz timegm timer-time timespec-add timespec-sub unsetenv update-copyright utimens vla warnings
MOSTLYCLEANFILES += core *.stackdump
......@@ -151,6 +151,14 @@ EXTRA_DIST += close-stream.h
## end gnulib module close-stream
## begin gnulib module count-leading-zeros
libgnu_a_SOURCES += count-leading-zeros.c
EXTRA_DIST += count-leading-zeros.h
## end gnulib module count-leading-zeros
## begin gnulib module count-one-bits
libgnu_a_SOURCES += count-one-bits.c
......
# count-leading-zeros.m4 serial 2
dnl Copyright (C) 2012-2017 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.
AC_DEFUN([gl_COUNT_LEADING_ZEROS],
[
dnl We don't need (and can't compile) count_leading_zeros_ll
dnl unless the type 'unsigned long long int' exists.
AC_REQUIRE([AC_TYPE_UNSIGNED_LONG_LONG_INT])
])
......@@ -54,6 +54,7 @@ AC_DEFUN([gl_EARLY],
# Code from module careadlinkat:
# Code from module clock-time:
# Code from module close-stream:
# Code from module count-leading-zeros:
# Code from module count-one-bits:
# Code from module count-trailing-zeros:
# Code from module crypto/md5:
......@@ -190,6 +191,7 @@ AC_DEFUN([gl_INIT],
gl_CLOCK_TIME
gl_CLOSE_STREAM
gl_MODULE_INDICATOR([close-stream])
gl_COUNT_LEADING_ZEROS
gl_COUNT_ONE_BITS
gl_COUNT_TRAILING_ZEROS
gl_MD5
......@@ -871,6 +873,8 @@ AC_DEFUN([gl_FILE_LIST], [
lib/careadlinkat.h
lib/close-stream.c
lib/close-stream.h
lib/count-leading-zeros.c
lib/count-leading-zeros.h
lib/count-one-bits.c
lib/count-one-bits.h
lib/count-trailing-zeros.c
......@@ -1000,6 +1004,7 @@ AC_DEFUN([gl_FILE_LIST], [
m4/c-strtod.m4
m4/clock_time.m4
m4/close-stream.m4
m4/count-leading-zeros.m4
m4/count-one-bits.m4
m4/count-trailing-zeros.m4
m4/dirent_h.m4
......
......@@ -45,6 +45,8 @@ along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>. */
#include <math.h>
#include <count-leading-zeros.h>
/* 'isfinite' and 'isnan' cause build failures on Solaris 10 with the
bundled GCC in c99 mode. Work around the bugs with simple
implementations that are good enough. */
......@@ -290,28 +292,46 @@ DEFUN ("float", Ffloat, Sfloat, 1, 1, 0,
return arg;
}
static int
ecount_leading_zeros (EMACS_UINT x)
{
return (EMACS_UINT_WIDTH == UINT_WIDTH ? count_leading_zeros (x)
: EMACS_UINT_WIDTH == ULONG_WIDTH ? count_leading_zeros_l (x)
: count_leading_zeros_ll (x));
}
DEFUN ("logb", Flogb, Slogb, 1, 1, 0,
doc: /* Returns largest integer <= the base 2 log of the magnitude of ARG.
This is the same as the exponent of a float. */)
(Lisp_Object arg)
{
Lisp_Object val;
EMACS_INT value;
double f = extract_float (arg);
CHECK_NUMBER_OR_FLOAT (arg);
if (f == 0.0)
value = MOST_NEGATIVE_FIXNUM;
else if (isfinite (f))
if (FLOATP (arg))
{
int ivalue;
frexp (f, &ivalue);
value = ivalue - 1;
double f = XFLOAT_DATA (arg);
if (f == 0)
value = MOST_NEGATIVE_FIXNUM;
else if (isfinite (f))
{
int ivalue;
frexp (f, &ivalue);
value = ivalue - 1;
}
else
value = MOST_POSITIVE_FIXNUM;
}
else
value = MOST_POSITIVE_FIXNUM;
{
EMACS_INT i = eabs (XINT (arg));
value = (i == 0
? MOST_NEGATIVE_FIXNUM
: EMACS_UINT_WIDTH - 1 - ecount_leading_zeros (i));
}
XSETINT (val, value);
return val;
return make_number (value);
}
......
......@@ -80,19 +80,19 @@ DEFINE_GDB_SYMBOL_END (GCTYPEBITS)
# elif INTPTR_MAX <= INT_MAX && !defined WIDE_EMACS_INT
typedef int EMACS_INT;
typedef unsigned int EMACS_UINT;
enum { EMACS_INT_WIDTH = INT_WIDTH };
enum { EMACS_INT_WIDTH = INT_WIDTH, EMACS_UINT_WIDTH = UINT_WIDTH };
# define EMACS_INT_MAX INT_MAX
# define pI ""
# elif INTPTR_MAX <= LONG_MAX && !defined WIDE_EMACS_INT
typedef long int EMACS_INT;
typedef unsigned long EMACS_UINT;
enum { EMACS_INT_WIDTH = LONG_WIDTH };
enum { EMACS_INT_WIDTH = LONG_WIDTH, EMACS_UINT_WIDTH = ULONG_WIDTH };
# define EMACS_INT_MAX LONG_MAX
# define pI "l"
# elif INTPTR_MAX <= LLONG_MAX
typedef long long int EMACS_INT;
typedef unsigned long long int EMACS_UINT;
enum { EMACS_INT_WIDTH = LLONG_WIDTH };
enum { EMACS_INT_WIDTH = LLONG_WIDTH, EMACS_UINT_WIDTH = ULLONG_WIDTH };
# define EMACS_INT_MAX LLONG_MAX
# ifdef __MINGW32__
# define pI "I64"
......
......@@ -25,4 +25,7 @@
(should-error (round most-negative-fixnum -1.0))
(should-error (truncate most-negative-fixnum -1.0)))
(ert-deftest logb-extreme-fixnum ()
(should (= (logb most-negative-fixnum) (1+ (logb most-positive-fixnum)))))
(provide 'floatfns-tests)
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