Yukihiro "Matz" Matsumoto 4507b4a633 mruby-bigint: gate mpz_mod's Barrett path on the algorithm's precondition ...

Barrett reduction requires x < 2^(2*bits(m)); the gate condition only
required x->sz >= y->sz + 2, which let x.sz reach 25 limbs against a
4-limb modulus. When the precondition is violated, mpz_barrett_reduce
silently truncates high limbs and returns garbage.

Integer#remainder, which routes through mpz_mod, was affected:
(3**500).remainder((2**100)+3) returned the wrong value. Integer#%
took the udiv path via mpz_mmod and was unaffected.

Add x->sz <= 2 * y->sz to the gate so out-of-range inputs fall
through to the general udiv path.

Co-authored-by: Claude <noreply@anthropic.com>

2026-05-22 07:08:26 +09:00

..

bigint.rb

mruby-bigint: gate mpz_mod's Barrett path on the algorithm's precondition

2026-05-22 07:08:26 +09:00