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Merged
sergio-correia merged 1 commit into from
Jul 23, 2026
Merged

b64: speed up encode/decode with lookup tables #185

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68 changes: 44 additions & 24 deletions lib/b64.c
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,23 @@ typedef struct {

static const char *map = JOSE_B64_MAP;

/* Reverse of JOSE_B64_MAP: stored value is (index + 1); 0 means invalid.
* Must stay consistent with JOSE_B64_MAP in <jose/b64.h>; tests/api_b64.c
* exhaustively verifies this. */
static const uint8_t unmap[256] = {
['A']= 1,['B']= 2,['C']= 3,['D']= 4,['E']= 5,['F']= 6,['G']= 7,['H']= 8,
['I']= 9,['J']=10,['K']=11,['L']=12,['M']=13,['N']=14,['O']=15,['P']=16,
['Q']=17,['R']=18,['S']=19,['T']=20,['U']=21,['V']=22,['W']=23,['X']=24,
['Y']=25,['Z']=26,
['a']=27,['b']=28,['c']=29,['d']=30,['e']=31,['f']=32,['g']=33,['h']=34,
['i']=35,['j']=36,['k']=37,['l']=38,['m']=39,['n']=40,['o']=41,['p']=42,
['q']=43,['r']=44,['s']=45,['t']=46,['u']=47,['v']=48,['w']=49,['x']=50,
['y']=51,['z']=52,
['0']=53,['1']=54,['2']=55,['3']=56,['4']=57,['5']=58,['6']=59,['7']=60,
['8']=61,['9']=62,
['-']=63,['_']=64,
};

static size_t
b64_dlen(size_t elen)
{
Expand Down Expand Up @@ -214,7 +231,6 @@ jose_b64_dec_io(jose_io_t *next)
size_t
jose_b64_dec_buf(const void *i, size_t il, void *o, size_t ol)
{
const size_t len = strlen(map);
const char *e = i;
uint8_t *d = o;
uint8_t rem = 0;
Expand All @@ -230,14 +246,13 @@ jose_b64_dec_buf(const void *i, size_t il, void *o, size_t ol)
return SIZE_MAX;

for (size_t io = 0; io < il; io++) {
uint8_t v = 0;

for (const char c = e[io]; v < len && c != map[v]; v++)
continue;
uint8_t v = unmap[(uint8_t) e[io]];

if (v >= len)
if (v == 0)
return SIZE_MAX;

v -= 1; /* recover the real 0..63 value */

switch (io % JOSE_B64_ENC_BLK) {
case 0:
if (!e[io+1] || rem > 0)
Expand Down Expand Up @@ -339,8 +354,8 @@ size_t
jose_b64_enc_buf(const void *i, size_t il, void *o, size_t ol)
{
const uint8_t *ib = i;
uint8_t rem = 0;
size_t oo = 0;
size_t io = 0;
char *ob = o;

if (!o)
Expand All @@ -349,25 +364,30 @@ jose_b64_enc_buf(const void *i, size_t il, void *o, size_t ol)
if (ol < b64_elen(il))
return SIZE_MAX;

for (size_t io = 0; io < il; io++) {
uint8_t c = ib[io];

switch (io % 3) {
case 0:
ob[oo++] = map[c >> 2];
ob[oo++] = map[rem = (c & 0b11) << 4];
break;
/* Consume whole 3-byte blocks: 24 bits -> four 6-bit map[] lookups. */
for (; io + JOSE_B64_DEC_BLK <= il; io += JOSE_B64_DEC_BLK) {
uint32_t n = (uint32_t) ib[io] << 16
| (uint32_t) ib[io+1] << 8
| (uint32_t) ib[io+2];

case 1:
ob[oo-1] = map[rem | (c >> 4)];
ob[oo++] = map[rem = (c & 0b1111) << 2];
break;
ob[oo++] = map[(n >> 18) & 0x3f];
ob[oo++] = map[(n >> 12) & 0x3f];
ob[oo++] = map[(n >> 6) & 0x3f];
ob[oo++] = map[ n & 0x3f];
}

case 2:
ob[oo-1] = map[rem | (c >> 6)];
ob[oo++] = map[c & 0b111111];
break;
}
/* Handle the trailing 1 or 2 bytes (unpadded base64url). */
switch (il - io) {
case 2:
ob[oo++] = map[ib[io] >> 2];
ob[oo++] = map[(ib[io] & 0b11) << 4 | (ib[io+1] >> 4)];
ob[oo++] = map[(ib[io+1] & 0b1111) << 2];
break;

case 1:
ob[oo++] = map[ib[io] >> 2];
ob[oo++] = map[(ib[io] & 0b11) << 4];
break;
}

return oo;
Expand Down
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