Silence off cython's warning compiling element_givaro.pyx

[ClementPernet]

While compiling sage-8.0beta4, I saw a bunch of warnings (which could have been here for a while):

[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:313:49: local variable 'res' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:389:46: local variable 'res' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:394:42: local variable 'res' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:398:42: local variable 'res' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:498:34: local variable 'g' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:532:32: local variable 'r' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:534:16: local variable 'r' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:562:30: local variable 'r' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:564:16: local variable 'r' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:717:33: local variable 'r' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:736:33: local variable 'r' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:756:35: local variable 'r' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:1110:39: local variable 'r' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:1127:39: local variable 'r' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:1150:39: local variable 'r' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:1167:39: local variable 'r' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:1184:39: local variable 'r' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:1217:35: local variable 'r' referenced before assignment
[sagelib-8.0.beta4] warning: sage/rings/finite_rings/element_givaro.pyx:1218:59: local variable 'r' referenced before assignment
[

Basically, the variables are passed as "out" arguments, and cython complains that they are not initialized, which is fine, but Cython has no way to know it. It is safe to force their value to 0 at declaration (e.g. int res = 0;) and this would silence off the warnings.

CC: @videlec

Component: basic arithmetic

Issue created by migration from https://trac.sagemath.org/ticket/22966

[jdemeyer]

comment:1

I consider the warnings a Cython bug. I am not sure that there is anything to be done in Sage.