py/mpz: Fix bug with overflowing C-shift in division routine.
When DIG_SIZE=32, a uint32_t is used to store limbs, and no normalisation is needed because the MSB is already set, then there will be left and right shifts (in C) by 32 of a 32-bit variable, leading to undefined behaviour. This patch fixes this bug.
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py/mpz.c
8
py/mpz.c
@ -491,7 +491,7 @@ STATIC void mpn_div(mpz_dig_t *num_dig, mp_uint_t *num_len, mpz_dig_t *den_dig,
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for (mpz_dig_t *den = den_dig, carry = 0; den < den_dig + den_len; ++den) {
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mpz_dig_t d = *den;
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*den = ((d << norm_shift) | carry) & DIG_MASK;
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carry = d >> (DIG_SIZE - norm_shift);
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carry = (mpz_dbl_dig_t)d >> (DIG_SIZE - norm_shift);
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}
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// now need to shift numerator by same amount as denominator
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@ -501,7 +501,7 @@ STATIC void mpn_div(mpz_dig_t *num_dig, mp_uint_t *num_len, mpz_dig_t *den_dig,
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for (mpz_dig_t *num = num_dig, carry = 0; num < num_dig + *num_len; ++num) {
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mpz_dig_t n = *num;
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*num = ((n << norm_shift) | carry) & DIG_MASK;
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carry = n >> (DIG_SIZE - norm_shift);
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carry = (mpz_dbl_dig_t)n >> (DIG_SIZE - norm_shift);
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}
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// cache the leading digit of the denominator
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@ -618,14 +618,14 @@ STATIC void mpn_div(mpz_dig_t *num_dig, mp_uint_t *num_len, mpz_dig_t *den_dig,
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for (mpz_dig_t *den = den_dig + den_len - 1, carry = 0; den >= den_dig; --den) {
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mpz_dig_t d = *den;
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*den = ((d >> norm_shift) | carry) & DIG_MASK;
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carry = d << (DIG_SIZE - norm_shift);
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carry = (mpz_dbl_dig_t)d << (DIG_SIZE - norm_shift);
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}
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// unnormalise numerator (remainder now)
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for (mpz_dig_t *num = orig_num_dig + *num_len - 1, carry = 0; num >= orig_num_dig; --num) {
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mpz_dig_t n = *num;
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*num = ((n >> norm_shift) | carry) & DIG_MASK;
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carry = n << (DIG_SIZE - norm_shift);
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carry = (mpz_dbl_dig_t)n << (DIG_SIZE - norm_shift);
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}
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// strip trailing zeros
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@ -1,3 +1,10 @@
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for lhs in (1000000000000000000000000, 10000000000100000000000000, 10012003400000000000000007, 12349083434598210349871029923874109871234789):
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for rhs in range(1, 555):
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print(lhs // rhs)
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# these check an edge case on 64-bit machines where two mpz limbs
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# are used and the most significant one has the MSB set
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x = 0x8000000000000000
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print((x + 1) // x)
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x = 0x86c60128feff5330
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print((x + 1) // x)
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@ -8,3 +8,10 @@ for i in range(11):
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y = delta * (j)# - 5) # TODO reinstate negative number test when % is working with sign correctly
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if y != 0:
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print(x % y)
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# these check an edge case on 64-bit machines where two mpz limbs
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# are used and the most significant one has the MSB set
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x = 0x8000000000000000
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print((x + 1) % x)
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x = 0x86c60128feff5330
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print((x + 1) % x)
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