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Implement "_multi" variants of shift functions...

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...also fix up the implementation of `ccn_div_euclid`
This commit is contained in:
Ariel Abreu 2020-03-22 14:49:23 -04:00
parent f60615dce8
commit 8fd95879e4
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GPG Key ID: 6EA25D8348CAA137
2 changed files with 46 additions and 13 deletions
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3
.gitignore vendored
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@ -1 +1,2 @@
build
build
.vscode

56
src/ccn.c
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@ -32,8 +32,20 @@ cc_unit ccn_shift_right(cc_size n, cc_unit* r, const cc_unit* s, size_t k) {
return carry;
}
void ccn_shift_right_multi(cc_size n, cc_unit *r, const cc_unit *s, size_t k) {
printf("DARLING CRYPTO STUB: %s\n", __PRETTY_FUNCTION__);
void ccn_shift_right_multi(cc_size n, cc_unit* r, const cc_unit* s, size_t k) {
cc_size discarded_units = k / CCN_UNIT_BITS;
k -= discarded_units * CCN_UNIT_BITS;
cc_unit carry = 0;
cc_unit temp;
for (cc_size i = n; i > discarded_units; --i) {
temp = s[i - 1];
r[(i - 1) - discarded_units] = temp >> k;
r[(i - 1) - discarded_units] |= carry;
if (i > n - discarded_units)
r[i - 1] = 0;
carry = temp << (CCN_UNIT_BITS - k);
}
}
/*
@ -55,8 +67,20 @@ cc_unit ccn_shift_left(cc_size n, cc_unit* r, const cc_unit* s, size_t k) {
return carry;
}
void ccn_shift_left_multi(cc_size n, cc_unit *r, const cc_unit *s, size_t k) {
printf("DARLING CRYPTO STUB: %s\n", __PRETTY_FUNCTION__);
void ccn_shift_left_multi(cc_size n, cc_unit* r, const cc_unit* s, size_t k) {
cc_size discarded_units = k / CCN_UNIT_BITS;
k -= discarded_units * CCN_UNIT_BITS;
cc_unit carry = 0;
cc_unit temp;
for (cc_size i = 0; i < n - discarded_units; ++i) {
temp = s[i];
r[i + discarded_units] = temp << k;
r[i + discarded_units] |= carry;
if (i < discarded_units)
r[i] = 0;
carry = temp >> (CCN_UNIT_BITS - k);
}
}
size_t ccn_bitlen(cc_size n, const cc_unit *s) {
@ -494,8 +518,6 @@ int ccn_div_euclid(cc_size nq, cc_unit *q, cc_size nr, cc_unit *r, cc_size na, c
// NOTE(@facekapow):
// i actually haven't tested this implementation
cc_unit* tmp_remainder = NULL;
na = ccn_n(na, a);
nd = ccn_n(nd, d);
@ -509,8 +531,20 @@ int ccn_div_euclid(cc_size nq, cc_unit *q, cc_size nr, cc_unit *r, cc_size na, c
if (nr < nd)
return -1;
if (na < nd) {
if (r)
ccn_set(na, r, a);
if (q)
ccn_zero(nq, q);
return 0;
}
cc_unit* tmp_d = __builtin_alloca(ccn_sizeof_n(na));
memset(tmp_d, 0, ccn_sizeof_n(na));
ccn_set(nd, tmp_d, d);
// if the divisor is greater, we cannot divide!
if (ccn_cmpn(na, a, nd, d) < 0) {
if (ccn_cmp(na, a, tmp_d) < 0) {
// note that here it is ok to copy a into r
// even though r's size depends on that of d
// because we've determined that d is bigger than a
@ -521,17 +555,15 @@ int ccn_div_euclid(cc_size nq, cc_unit *q, cc_size nr, cc_unit *r, cc_size na, c
return 0;
}
tmp_remainder = __builtin_alloca(ccn_sizeof_n(na));
cc_unit* tmp_remainder = __builtin_alloca(ccn_sizeof_n(na));
ccn_set(na, tmp_remainder, a);
cc_size tmp_remainder_curr_n = 0;
// we do ccn_n on every loop because ccn_cmpn looks at both n's and says one value is greater
// than the other just based on the n's. therefore, if we want to check for real whether the
// remainder is greater than the divisor, we need to check how many n's are actually used
while (ccn_cmpn(tmp_remainder_curr_n = ccn_n(na, tmp_remainder), tmp_remainder, nd, d) >= 0) {
ccn_subn(tmp_remainder_curr_n, tmp_remainder, tmp_remainder, nd, d);
while (ccn_cmp(na, tmp_remainder, tmp_d) >= 0) {
ccn_sub(na, tmp_remainder, tmp_remainder, tmp_d);
if (q)
ccn_add1(nq, q, q, 1);
}