urbit/shrub
1
1
Fork 0
mirror of https://github.com/urbit/shrub.git synced 2024-12-19 00:13:12 +03:00
Code Issues Packages Projects Releases Wiki Activity

ur: optimizes bitstream bytes-reader implementation

Browse Source
This commit is contained in:
Joe Bryan 2022-09-14 19:35:34 -04:00
parent 29bce64669
commit dbda9ed30c
1 changed files with 10 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
pkg/urbit/ur/bitstream.c
View File

@ -411,25 +411,21 @@ ur_bsr_bytes_any(ur_bsr_t *bsr, uint64_t len, uint8_t *out)
//
else {
uint8_t rest = 8 - off;
uint8_t mask = (1 << off) - 1;
uint8_t byt, l, m = *b >> off;
uint64_t last = left - 1;
uint64_t max = ur_min(last, len_byt);
uint8_t m, l;
// loop over all the bytes we need (or all that remain)
//
// [l] holds [off] bits
// [m] holds [rest] bits
//
{
uint64_t max = ur_min(last, len_byt);
uint64_t i;
for ( i = 0; i < max; i++ ) {
byt = *++b;
l = byt & mask;
out[i] = m ^ (l << rest);
m = byt >> off;
out[i] = (b[i] >> off) ^ (b[i + 1] << rest);
}
b += max;
m = *b >> off;
}
// we're reading into or beyond the last byte [bsr]
@ -441,13 +437,13 @@ ur_bsr_bytes_any(ur_bsr_t *bsr, uint64_t len, uint8_t *out)
uint8_t bits = len - (last << 3);
if ( bits < rest ) {
out[last] = m & ((1 << bits) - 1);
out[max] = m & ((1 << len_bit) - 1);
bsr->bytes = b;
left = 1;
off += len_bit;
}
else {
out[last] = m;
out[max] = m;
bsr->bytes = 0;
left = 0;
off = 0;
@ -465,11 +461,11 @@ ur_bsr_bytes_any(ur_bsr_t *bsr, uint64_t len, uint8_t *out)
if ( len_bit ) {
if ( len_bit <= rest ) {
out[len_byt] = m & ((1 << len_bit) - 1);
out[max] = m & ((1 << len_bit) - 1);
}
else {
l = *++b & ((1 << off) - 1);
out[len_byt] = m ^ (l << rest);
out[max] = (m ^ (l << rest)) & ((1 << len_bit) - 1);
}
}
}