root/src/base64.c

DEFINITIONS

1. base64_encode
2. base64_decode

#include <string.h>

char b64string[] =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

long base64_encode (to, from, len)
        char *to, *from;
        unsigned int len;
{
        char *fromp = from;
        char *top = to;
        unsigned char cbyte;
        unsigned char obyte;
        char end[3];

        for (; len >= 3; len -= 3) {
                cbyte = *fromp++;
                *top++ = b64string[(int)(cbyte >> 2)];
                obyte = (cbyte << 4) & 0x30;            /* 0011 0000 */

                cbyte = *fromp++;
                obyte |= (cbyte >> 4);                  /* 0000 1111 */
                *top++ = b64string[(int)obyte];
                obyte = (cbyte << 2) & 0x3C;            /* 0011 1100 */

                cbyte = *fromp++;
                obyte |= (cbyte >> 6);                  /* 0000 0011 */
                *top++ = b64string[(int)obyte];
                *top++ = b64string[(int)(cbyte & 0x3F)];/* 0011 1111 */
        }

        if (len) {
                end[0] = *fromp++;
                if (--len) end[1] = *fromp++; else end[1] = 0;
                end[2] = 0;

                cbyte = end[0];
                *top++ = b64string[(int)(cbyte >> 2)];
                obyte = (cbyte << 4) & 0x30;            /* 0011 0000 */

                cbyte = end[1];
                obyte |= (cbyte >> 4);
                *top++ = b64string[(int)obyte];
                obyte = (cbyte << 2) & 0x3C;            /* 0011 1100 */

                if (len) *top++ = b64string[(int)obyte];
                else *top++ = '=';
                *top++ = '=';
        }
        *top = 0;
        return top - to;
}

/* badchar(): check if c is decent; puts either the */
/* location of c or null into p.                  */
#define badchar(c,p) (!(p = memchr(b64string, c, 64)))

long base64_decode (to, from, len)
        char *to, *from;
        unsigned int len;
{
        char *fromp = from;
        char *top = to;
        char *p;
        unsigned char cbyte;
        unsigned char obyte;
        int padding = 0;

        for (; len >= 4; len -= 4) {
                if ((cbyte = *fromp++) == '=') cbyte = 0;
                else {
                        if (badchar(cbyte, p)) return -1;
                        cbyte = (p - b64string);
                }
                obyte = cbyte << 2;             /* 1111 1100 */

                if ((cbyte = *fromp++) == '=') cbyte = 0;
                else {
                        if (badchar(cbyte, p)) return -1;
                        cbyte = p - b64string;
                }
                obyte |= cbyte >> 4;            /* 0000 0011 */
                *top++ = obyte;

                obyte = cbyte << 4;             /* 1111 0000 */
                if ((cbyte = *fromp++) == '=') { cbyte = 0; padding++; }
                else {
                        padding = 0;
                        if (badchar (cbyte, p)) return -1;
                        cbyte = p - b64string;
                }
                obyte |= cbyte >> 2;            /* 0000 1111 */
                *top++ = obyte;

                obyte = cbyte << 6;             /* 1100 0000 */
                if ((cbyte = *fromp++) == '=') { cbyte = 0; padding++; }
                else {
                        padding = 0;
                        if (badchar (cbyte, p)) return -1;
                        cbyte = p - b64string;
                }
                obyte |= cbyte;                 /* 0011 1111 */
                *top++ = obyte;
        }

        *top = 0;
        if (len) return -1;
        return (top - to) - padding;
}