diff options
| -rw-r--r-- | src/bignum.h | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/src/bignum.h b/src/bignum.h index 3716c49656..5190c2f390 100644 --- a/src/bignum.h +++ b/src/bignum.h @@ -131,7 +131,15 @@ public: if (sn < (int64)0) { - n = -sn; + // 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; fNegative = true; } else { n = sn; |