Opened 9 years ago

Closed 8 years ago

## #631 closed proposed feature (fixed)

# detect exponent overflows for polynomial operations

Reported by: | Owned by: | somebody | |
---|---|---|---|

Priority: | minor | Milestone: | 4-1-0 and higher |

Component: | dontKnow | Version: | 4-0-0 |

Keywords: | overflow polynomial operations | Cc: |

### Description

overflow hell:

ring rng = 0,(x,y),dp; > short = 0 ; > . poly f = x^1073741823; > subst(f,x,x^3); // ** undetected overflow ** x^3221225469*y^4294967295 > . f = x^2147483647; > poly g = f*f; > . g*x*x; // ok ? OVERFLOW in mult(d=4294967295, d=1, max=4294967295) ? error occurred in or before STDIN line 12: `g*x*x; // ok` > . ideal J = g*x; > J*x; // ** undetected overflow ** _[1]=y > J*J; // ** undetected overflow ** _[1]=x^4294967294*y > . poly h = x^2147483647; > . h = h*x; > ideal I = h; > subst(I,x,x^2); // ok // ** possible OVERFLOW in subst, max exponent is 4294967295 _[1]=1 > . ring G = 0,(a,b),dp; > ideal phi = a,b; > map m = rng,a^2,b; > m(I); // ** undetected overflow ** _[1]=1

input:

ring rng = 0,(x,y),dp; poly f = x^1073741823; subst(f,x,x^3); f = x^2147483647; poly g = f*f; g*x*x; // ok ideal J = g*x; J*x; J*J; poly h = x^2147483647; h = h*x; ideal I = h; subst(I,x,x^2); // ok ring G = 0,(a,b),dp; ideal phi = a,b; map m = rng,a^2,b; m(I);

Question: are other overflow issues known? May the same happen in 'factory'?

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partially duplicate to tr. #696, fix and test there.

Comments: factory is not involved: no degree-increasing routines of factory can be reached