TonBERRY/micropython
3
0
Fork 0
Code Pull Requests Activity

py/mpz: Fix bugs with bitwise of -0 by ensuring all 0's are positive.

Browse Source 
This commit makes sure that the value zero is always encoded in an mpz_t as
neg=0 and len=0 (previously it was just len=0).

This invariant is needed for some of the bitwise operations that operate on
negative numbers, because they cannot handle -0.  For example
(-((1<<100)-(1<<100)))|1 was being computed as -65535, instead of 1.

Fixes issue #8042.

Signed-off-by: Damien George <damien@micropython.org>
This commit is contained in:
Damien George
2021-11-30 00:31:46 +11:00
parent 05bea70979
commit 2c139bbf4e
3 changed files with 52 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

19
py/mpz.c
View File

@@ -713,6 +713,7 @@ void mpz_set(mpz_t *dest, const mpz_t *src) {
void mpz_set_from_int(mpz_t *z, mp_int_t val) {
if (val == 0) {
z->neg = 0;
z->len = 0;
return;
}
@@ -899,10 +900,6 @@ bool mpz_is_even(const mpz_t *z) {
#endif
int mpz_cmp(const mpz_t *z1, const mpz_t *z2) {
// to catch comparison of -0 with +0
if (z1->len == 0 && z2->len == 0) {
return 0;
}
int cmp = (int)z2->neg - (int)z1->neg;
if (cmp != 0) {
return cmp;
@@ -1052,7 +1049,9 @@ void mpz_neg_inpl(mpz_t *dest, const mpz_t *z) {
if (dest != z) {
mpz_set(dest, z);
}
dest->neg = 1 - dest->neg;
if (dest->len) {
dest->neg = 1 - dest->neg;
}
}
/* computes dest = ~z (= -z - 1)
@@ -1148,7 +1147,7 @@ void mpz_add_inpl(mpz_t *dest, const mpz_t *lhs, const mpz_t *rhs) {
dest->len = mpn_sub(dest->dig, lhs->dig, lhs->len, rhs->dig, rhs->len);
}
dest->neg = lhs->neg;
dest->neg = lhs->neg & !!dest->len;
}
/* computes dest = lhs - rhs
@@ -1172,7 +1171,9 @@ void mpz_sub_inpl(mpz_t *dest, const mpz_t *lhs, const mpz_t *rhs) {
dest->len = mpn_sub(dest->dig, lhs->dig, lhs->len, rhs->dig, rhs->len);
}
if (neg) {
if (dest->len == 0) {
dest->neg = 0;
} else if (neg) {
dest->neg = 1 - lhs->neg;
} else {
dest->neg = lhs->neg;
@@ -1484,14 +1485,16 @@ void mpz_divmod_inpl(mpz_t *dest_quo, mpz_t *dest_rem, const mpz_t *lhs, const m
mpz_need_dig(dest_quo, lhs->len + 1); // +1 necessary?
memset(dest_quo->dig, 0, (lhs->len + 1) * sizeof(mpz_dig_t));
dest_quo->neg = 0;
dest_quo->len = 0;
mpz_need_dig(dest_rem, lhs->len + 1); // +1 necessary?
mpz_set(dest_rem, lhs);
mpn_div(dest_rem->dig, &dest_rem->len, rhs->dig, rhs->len, dest_quo->dig, &dest_quo->len);
dest_rem->neg &= !!dest_rem->len;
// check signs and do Python style modulo
if (lhs->neg != rhs->neg) {
dest_quo->neg = 1;
dest_quo->neg = !!dest_quo->len;
if (!mpz_is_zero(dest_rem)) {
mpz_t mpzone;
mpz_init_from_int(&mpzone, -1);