diff options
| -rw-r--r-- | src/bignum.h | 12 |
1 files changed, 3 insertions, 9 deletions
diff --git a/src/bignum.h b/src/bignum.h index 5190c2f390..74f657b567 100644 --- a/src/bignum.h +++ b/src/bignum.h @@ -131,15 +131,9 @@ public: if (sn < (int64)0) { - // We negate in 2 steps to avoid signed subtraction overflow, - // i.e. -(-2^63), which is an undefined operation and causes SIGILL - // when compiled with -ftrapv. - // - // Note that uint64_t n = sn, when sn is an int64_t, is a - // well-defined operation and n will be equal to sn + 2^64 when sn - // is negative. - n = sn; - n = -n; + // Since the minimum signed integer cannot be represented as positive so long as its type is signed, and it's not well-defined what happens if you make it unsigned before negating it, we instead increment the negative integer by 1, convert it, then increment the (now positive) unsigned integer by 1 to compensate + n = -(sn + 1); + ++n; fNegative = true; } else { n = sn; |