Description:
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Distro: openSUSE Leap 42.1 (x86_64)

Packages used:
  php7-7.0.15-35.2.x86_64
  php7-gmp-7.0.15-35.2.x86_64

Standard (not changed) php.ini

Description:
The function gmp_export() gives wrong result for certain input: if the argument supplied is 0 or gmp_init(0) then gmp_export() outputs empty string.

Test script:
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<?php
echo gmp_export(         0 );  // will output '', must be "\x0"
echo gmp_export(gmp_init(0));  // will output '', must be "\x0"