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megolm_advance_to: Remove excessive optimisation

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There was some slightly overcomplex logic designed to save a couple of hash
operations when R(0) and R(1) were advanced, but the extra code was hard to
understand and didn't save much.
This commit is contained in:
Richard van der Hoff 2016-05-24 16:58:51 +01:00
parent ef8d24f483
commit 1f31427139
1 changed files with 7 additions and 22 deletions
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29
src/megolm.c
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@ -106,6 +106,7 @@ void megolm_advance_to(Megolm *megolm, uint32_t advance_to) {
for (j = 0; j < (int)MEGOLM_RATCHET_PARTS; j++) {
int shift = (MEGOLM_RATCHET_PARTS-j-1) * 8;
uint32_t mask = (~(uint32_t)0) << shift;
int k;
/* how many times to we need to rehash this part? */
int steps = (advance_to >> shift) - (megolm->counter >> shift);
@ -122,30 +123,14 @@ void megolm_advance_to(Megolm *megolm, uint32_t advance_to) {
steps --;
}
/* on the last step (except for j=3), we need to bump at least R(j+1);
* depending on the target count, we may also need to bump R(j+2) and
* R(j+3).
/* on the last step we also need to bump R(j+1)...R(3).
*
* (Theoretically, we could skip bumping R(j+2) if we're going to bump
* R(j+1) again, but the code to figure that out is a bit baroque and
* doesn't save us much).
*/
int k;
switch(j) {
case 0:
if (!(advance_to & 0xFFFF00)) { k = 3; }
else if (!(advance_to & 0xFF00)) { k = 2; }
else { k = 1; }
break;
case 1:
if (!(advance_to & 0xFF00)) { k = 3; }
else { k = 2; }
break;
case 2:
case 3:
k = 3;
break;
}
while (k >= j) {
for (k = 3; k >= j; k--) {
rehash_part(megolm->data, j, k);
k--;
}
megolm->counter = advance_to & mask;
}