use an easier to understand base32 decoder

diff --git a/otp.c b/otp.c
index de06a61e3aae41f45330ebe8e07de1be383c8ca6..1584d304b8815eae5cf9714c2f7cdddc3d740482 100644 (file)
--- a/otp.c
+++ b/otp.c
@@ -41,31 +41,56 @@ int concat(char *dest, size_t *dest_used, size_t dest_size, char *src) {
 
 int b32_decode(unsigned char *buf, size_t *len) {
        const char alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
-       size_t i = 0;
-       char x = 0, *ptr;
-       unsigned char *output = buf, count, lsh;
-       if(buf == NULL)
-               return -1;
-       for(count = 1;; count++) {
-               while(isspace(buf[i]))
+       size_t i = 0, used = 0;
+       unsigned char x, *output = buf;
+       char *ptr;
+       for(;;) {
+               while(isspace(buf[i]) || buf[i] == '\n')
                        i++;
-               if(buf[i] == '\0')
+               if(buf[i] == '\0' || buf[i] == '=')
                        break;
                ptr = strchr(alphabet, toupper(buf[i++]));
                if(ptr == NULL || *ptr == '\0')
                        return -1;
                x = ptr - alphabet;
-               if(x < 0)
-                       return -1;
-               lsh = (count * 3) % 8;
-               if(lsh > 3)
-                       *output |= x >> (8 - lsh);
-               if(lsh + (count > 1) > 3)
+               switch(used++ % 8) {
+               case 0:
+                       *output = x << 3;
+                       break;
+               case 1:
+                       *output |= x >> 2;
+                       output++;
+                       *output = x << 6;
+                       break;
+               case 2:
+                       *output |= x << 1;
+                       break;
+               case 3:
+                       *output |= x >> 4;
+                       output++;
+                       *output = x << 4;
+                       break;
+               case 4:
+                       *output |= x >> 1;
+                       output++;
+                       *output = x << 7;
+                       break;
+               case 5:
+                       *output |= x << 2;
+                       break;
+               case 6:
+                       *output |= x >> 3;
                        output++;
-               *output = (x << lsh) | ((lsh < 3) * *output);
+                       *output = x << 5;
+                       break;
+               case 7:
+                       *output |= x;
+                       output++;
+                       break;
+               }
        }
        if(len != NULL)
-               *len = output - buf + 1;
+               *len = output - buf;
        return 0;
 }