Created attachment 791502 [details]
Source file to mpz_gcdext() from libgmp

Description of problem:
GMP's function mpz_gcdext() returns unexpected results.

This library solves the equation format A*S + B*T = G

One test case that highlighted the error was:
INPUT A=345, B=34587345
OUTPUT S=-14436457, T=144, G=15
EXPECTED S=-601519, T=6, G=15


In order to trace the error

I found this problem while building PHP 5.5 from source, I ran into the following failed test:
gmp_yum gcdext() basic tests [ext/gmp/tests/022.phpt]

To isolate the problem to the library or to PHP, I borrowed the attached C program and ran the calculation and it returned the same values as PHP.

I then built the latest version of GMP (5.1.2) and reran the test. This time it produced the expected results:
OUTPUT S=-601519, T=6, G=15


Version-Release number of selected component (if applicable):
gmp-4.3.1-7.el6_2.2.x86_64


How reproducible:
Either the PHP build test or by compiling the attached test program. Since the test program is a lot faster that is included here.


Steps to Reproduce:
1. Run the following commands on a test system
    gcc -lgmp -o gmptest gmptest.c
    echo 345 > input
    echo 34587345 >> input
    ./gmptest < input


Actual results:
a = 345
b = 34587345
g = 15
s = -14436457
t = 144
g =? 15
a*s + b*t=g
345 * -14436457 + 34587345 * 144 = 15


Expected results:
a = 345
b = 34587345
g = 15
s = -601519
t = 6
g =? 15
a*s + b*t=g
345 * -601519 + 34587345 * 6 = 15