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Improved base64 decoder performance a little (using table)

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Bobbi Webber-Manners 2020-07-02 00:19:16 -04:00
parent 5b520be724
commit 9e97d399ac
1 changed files with 7 additions and 21 deletions
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28
apps/email.c
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@ -479,28 +479,14 @@ void decode_quoted_printable(FILE *fp, uint8_t binary) {
} }
/* /*
* Return value of character in Base64 encoding. * Base64 decode table
* Maybe a table is smaller/better?
*/ */
uint32_t base64_char(char c) { static const signed char base64_decode[] = {62,-1,-1,-1,63,52,53,54,55,56,57,58,59,60,61,-1,-1,-1,-2,-1,-1,-1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,-1,-1,-1,-1,-1,-1,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51};
if ((c >= 'A') && (c <= 'Z'))
return c - 'A';
if ((c >= 'a') && (c <= 'z'))
return c - 'a' + 26;
if ((c >= '0') && (c <= '9'))
return c - '0' + 52;
if (c == '+')
return 62;
if (c == '/')
return 63;
if (c == '=') // Padding
return 0;
return 0; // Should never happen
}
/* /*
* Decode linebuf[] from Base64 format and print on screen * Decode linebuf[] from Base64 format and print on screen
* Each line of base64 has up to 76 chars * Each line of base64 has up to 76 chars
* TODO This is hideously slow!!
*/ */
void decode_base64(FILE *fp, uint8_t binary) { void decode_base64(FILE *fp, uint8_t binary) {
uint16_t i = 0, j = 0; uint16_t i = 0, j = 0;
@ -514,10 +500,10 @@ void decode_base64(FILE *fp, uint8_t binary) {
fp = stdout; fp = stdout;
} }
while (linebuf[i] != '\r') { while (linebuf[i] != '\r') {
u.val = base64_char(linebuf[i]) << 18; u.val = (uint32_t)base64_decode[linebuf[i] - 43] << 18;
u.val |= base64_char(linebuf[i + 1]) << 12; u.val |= (uint32_t)base64_decode[linebuf[i + 1] - 43] << 12;
u.val |= base64_char(linebuf[i + 2]) << 6; u.val |= (uint32_t)base64_decode[linebuf[i + 2] - 43] << 6;
u.val |= base64_char(linebuf[i + 3]); u.val |= (uint32_t)base64_decode[linebuf[i + 3] - 43];
if (linebuf[i + 2] == '=') { if (linebuf[i + 2] == '=') {
// Two padding chars 'xx==' // Two padding chars 'xx=='
fputc(u.c[1], fp); fputc(u.c[1], fp);