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improve decode time

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atob() has been replaced with a lookup table, removing previous
conditionals and function calls necessary to decode.
This commit is contained in:
Eric 2025-05-29 16:02:45 +02:00
parent debab62506
commit aacf2324c7
3 changed files with 44 additions and 40 deletions
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76
encode.c
View file

@ -2,15 +2,35 @@
#define PADDING '=' #define PADDING '='
unsigned char b64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" \ static
"abcdefghijklmnopqrstuvwxyz" \ unsigned char b64toascii[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" \
"0123456789" \ "abcdefghijklmnopqrstuvwxyz" \
"+/"; "0123456789" \
"+/";
static
unsigned char b64urltoascii[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" \
"abcdefghijklmnopqrstuvwxyz" \
"0123456789" \
"-_";
static
unsigned char asciitob64[] = {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 62, 0, 62, 0, 63, 52, 53,
54, 55, 56, 57, 58, 59, 60, 61, 0, 0,
0, 0, 0, 0, 0, 0, 1, 2, 3, 4,
5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
25, 0, 0, 0, 0, 63, 0, 26, 27, 28,
29, 30, 31, 32, 33, 34, 35, 36, 37, 38,
39, 40, 41, 42, 43, 44, 45, 46, 47, 48,
49, 50, 51
};
unsigned char b64url[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" \
"abcdefghijklmnopqrstuvwxyz" \
"0123456789" \
"-_";
int int
encode(unsigned char *op, int olen, unsigned char *sp, int url) encode(unsigned char *op, int olen, unsigned char *sp, int url)
@ -20,7 +40,7 @@ encode(unsigned char *op, int olen, unsigned char *sp, int url)
unsigned char *sbeg; unsigned char *sbeg;
unsigned char *tend; unsigned char *tend;
table = (!url) ? b64 : b64url; table = (!url) ? b64toascii : b64urltoascii;
sbeg = sp; sbeg = sp;
tend = op + olen - (olen % 3); tend = op + olen - (olen % 3);
@ -52,52 +72,36 @@ encode(unsigned char *op, int olen, unsigned char *sp, int url)
} }
int int
decode(unsigned char *sp, int slen, unsigned char *op, int url) decode(unsigned char *sp, int slen, unsigned char *op)
{ {
int tmp, b, atob(int c, int url); int tmp, b;
unsigned char *obeg; unsigned char *obeg;
unsigned char *qend; unsigned char *qend;
obeg = op; obeg = op;
qend = sp + slen - (slen % 4); qend = sp + slen - (slen % 4);
while (sp < qend) { while (sp < qend) {
tmp = atob(*sp++, url) << 2; tmp = asciitob64[*sp++] << 2;
b = atob(*sp++, url); b = asciitob64[*sp++];
*op++ = tmp + ((b & ~15) >> 4); *op++ = tmp + ((b & ~15) >> 4);
tmp = (b & 15) << 4; tmp = (b & 15) << 4;
b = atob(*sp++, url); b = asciitob64[*sp++];
*op++ = tmp + ((b & ~3) >> 2); *op++ = tmp + ((b & ~3) >> 2);
*op++ = ((b & 3) << 6) + atob(*sp++, url); *op++ = ((b & 3) << 6) + asciitob64[*sp++];
} }
switch (slen % 4) { switch (slen % 4) {
case 3: case 3:
tmp = atob(*sp++, url) << 2; tmp = asciitob64[*sp++] << 2;
b = atob(*sp++, url); b = asciitob64[*sp++];
*op++ = tmp + ((b & ~15) >> 4); *op++ = tmp + ((b & ~15) >> 4);
tmp = (b & 15) << 4; tmp = (b & 15) << 4;
*op++ = tmp + ((atob(*sp++, url) & ~3) >> 2); *op++ = tmp + ((asciitob64[*sp++] & ~3) >> 2);
break; break;
case 2: case 2:
tmp = atob(*sp++, url) << 2; tmp = asciitob64[*sp++] << 2;
*op++ = tmp + ((atob(*sp++, url) & ~15) >> 4); *op++ = tmp + ((asciitob64[*sp++] & ~15) >> 4);
break; break;
} }
return op-obeg; return op-obeg;
} }
int atob(int c, int url)
{
if (c >= 'A' && c <= 'Z')
c -= 'A';
else if (c >= 'a' && c <= 'z')
c = c - 'a' + 26;
else if (c >= '0' && c <= '9')
c = c - '0' + 26 * 2;
else if (c == ((!url) ? '+' : '-'))
c = 62;
else
c = 63;
return c;
}

2
encode.h
View file

@ -5,6 +5,6 @@ int
encode(unsigned char *op, int olen, unsigned char *sp, int url); encode(unsigned char *op, int olen, unsigned char *sp, int url);
int int
decode(unsigned char *sp, int slen, unsigned char *op, int url); decode(unsigned char *sp, int slen, unsigned char *op);
#endif #endif

6
main.c
View file

@ -4,8 +4,8 @@
#include "output.h" #include "output.h"
#include "encode.h" #include "encode.h"
#define OCTETBUF 300 #define OCTETBUF 1500
#define SXTETBUF 400 #define SXTETBUF 2000
unsigned char obuf[OCTETBUF]; unsigned char obuf[OCTETBUF];
unsigned char sbuf[SXTETBUF]; unsigned char sbuf[SXTETBUF];
@ -54,7 +54,7 @@ main(int argc, char *argv[])
} }
if (dec) { if (dec) {
while ((n = readb((in) ? in : stdin, sbuf, SXTETBUF))) { while ((n = readb((in) ? in : stdin, sbuf, SXTETBUF))) {
n = decode(sbuf, n, obuf, url); n = decode(sbuf, n, obuf);
fwrite(obuf, sizeof(*obuf), n, (out) ? out : stdout); fwrite(obuf, sizeof(*obuf), n, (out) ? out : stdout);
} }
} else if (wrp) { } else if (wrp) {