You may have noted that the recent gmp update makes problems on some machines and two of the three reports come from Broadwell CPU. There is one thing that did indeed change with the update and that is use of the AVX ADC instruction on Broadwell/Skylake. Is it possible that somehow the stack model or some register save/restore is different on Cygwin that would produce that problem? I can only test on SandyBridge and IvyBridge for Intel and these have no problem.
Regards, Achim. -- +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+ DIY Stuff: http://Synth.Stromeko.net/DIY.html
