On Arch linux PHP 7.1.1 Everything is ok.

On php 5.4.39-0+deb7u2 

var_dump(is_infinite(-INF)); // true

See also: bug #73954

Fixed by https://github.com/php/php-src/commit/9ea0949f43959ff0cf519e7a10ef9de7a538cde3.

The fix in https://github.com/php/php-src/commit/714d825b62e719447686da6efe3b4063c2f25749 breaks the build for me for PHP 7.1.3 and PHP 7.0.17 branches:

The build fails with:

ext/filter/.libs/logical_filters.o: In function `php_filter_float':
/home/georgi/build/BUILD/php71-7.1.3/src/ext/filter/logical_filters.c:411: undefined reference to `isfinite'
ext/intl/collator/.libs/collator_is_numeric.o: In function `collator_is_numeric':
/home/georgi/build/BUILD/php71-7.1.3/src/ext/intl/collator/collator_is_numeric.c:255: undefined reference to `isfinite'
ext/standard/.libs/math.o: In function `zif_is_finite':
/home/georgi/build/BUILD/php71-7.1.3/src/ext/standard/math.c:589: undefined reference to `isfinite'
ext/standard/.libs/math.o: In function `_php_math_round':
/home/georgi/build/BUILD/php71-7.1.3/src/ext/standard/math.c:133: undefined reference to `isfinite'
/home/georgi/build/BUILD/php71-7.1.3/src/ext/standard/math.c:201: undefined reference to `isfinite'
ext/standard/.libs/var.o:/home/georgi/build/BUILD/php71-7.1.3/src/ext/standard/var.c:473: more undefined references to `isfinite' follow

After reverting 714d825b62e719447686da6efe3b4063c2f25749, I can build both 7.0 and 7.1 as before.

I can provide any logs necessary to track the problem. The build machine is CentOS 5.5 with glibc-devel-2.5-58.el5_6.3.

Does

#include <math.h>
#ifndef isfinite
# error Not defined
#endif
void main() {}

compile for you? This seems pretty weird, because glibc should have isfinite().

CentOS issue also reported in bug #74265.

The C example code does not compile on CentOS 5:

georgi@cent5:~$ cat > z.c
#include <math.h>
#ifndef isfinite
# error Not defined
#endif
void main() {}
georgi@cent5:~$ gcc z.c
z.c:3:3: error: #error Not defined
z.c: In function ‘main’:
z.c:5: warning: return type of ‘main’ is not ‘int’


georgi@cent5:~$ rpm -qa | grep glibc | sort | uniq
glibc-2.5-58.el5_6.3
glibc-common-2.5-58.el5_6.3
glibc-devel-2.5-58.el5_6.3
glibc-headers-2.5-58.el5_6.3

$ man isfinite 

says that isfinite() is a C99 feature. In order to see what's going on compiler diagnostics helps (please note that the return type of main is int according to all known standards):

main.c
------
#include <stdio.h>
#include <math.h>

int main()
{
   double d = 0;
   printf ("%d\n", isfinite (d));
   return 0;
}
------

   $ gcc -Wall -Werror main.c
   cc1: warnings being treated as errors
   main.c: In function 'main':
   main.c:7: error: implicit declaration of function 'isfinite'

The default mode of GCC is C99 since GCC 5, before it was C89. For those older compilers you have to explitly switch C99-mode on:

   $ gcc -Wall -Werror -std=c99 main.c

The reason why there is an linker error is that for the implicitly declared isfinite() the symbol is the object file and the symbol used in the libc is not "isfinite" but here on my machine "__finite":

   $ nm main.o
                    U __finite
   0000000000000000 T main
                    U printf