* @param nwords Length of bignum
* @return !v
*/
-static int zero(const unsigned long *v, int nwords) {
+static int zero(const uint32_t *v, int nwords) {
int n;
for(n = 0; n < nwords && !v[n]; ++n)
*
* The quotient is stored in @p v.
*/
-static unsigned divide(unsigned long *v, int nwords, unsigned long m) {
+static unsigned divide(uint32_t *v, int nwords, unsigned long m) {
unsigned long r = 0, a, b;
int n;
return r;
}
+/** @brief Multiple v by m and add a
+ * @param v Pointer to bigendian bignum
+ * @param nwords Length of bignum
+ * @param m Value to multiply by
+ * @param a Value to add
+ * @return 0 on success, non-0 on overflow
+ *
+ * Does v = m * v + a.
+ */
+static int mla(uint32_t *v, int nwords, uint32_t m, uint32_t a) {
+ int n = nwords - 1;
+ uint32_t carry = a;
+
+ while(n >= 0) {
+ const uint64_t p = (uint64_t)v[n] * m + carry;
+ carry = (uint32_t)(p >> 32);
+ v[n] = (uint32_t)p;
+ --n;
+ }
+ /* If there is still a carry then we overflowed */
+ return !!carry;
+}
+
+static const char basen_chars[] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
+
/** @brief Convert v to a chosen base
* @param v Pointer to bigendian bignum (modified!)
* @param nwords Length of bignum
* @return 0 on success, -1 if the buffer is too small
*
* Converts @p v to a string in the given base using decimal digits, lower case
- * letter sand upper case letters as digits.
+ * letters and upper case letters as digits.
+ *
+ * The inverse of nesab().
*/
-int basen(unsigned long *v,
+int basen(uint32_t *v,
int nwords,
char buffer[],
size_t bufsize,
unsigned base) {
size_t i = bufsize;
- static const char chars[] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
do {
if(i <= 1)
return -1; /* overflow */
- buffer[--i] = chars[divide(v, nwords, base)];
+ buffer[--i] = basen_chars[divide(v, nwords, base)];
} while(!zero(v, nwords));
memmove(buffer, buffer + i, bufsize - i);
buffer[bufsize - i] = 0;
return 0;
}
+/** @brief Convert a string back to a large integer in an arbitrary base
+ * @param v Where to store result as a bigendian bignum
+ * @param nwords Space available in @p v
+ * @param s Input string
+ * @param base Number base (2..62)
+ * @return 0 on success, non-0 on overflow or invalid input
+ *
+ * The inverse of basen(). If the number is much smaller than the buffer then
+ * the first words will be 0.
+ */
+int nesab(uint32_t *v,
+ int nwords,
+ const char *s,
+ unsigned base) {
+ /* Initialize to 0 */
+ memset(v, 0, nwords * sizeof *v);
+ while(*s) {
+ const char *dp = strchr(basen_chars, *s++);
+ if(!dp)
+ return -1;
+ if(mla(v, nwords, base, dp - basen_chars))
+ return -1;
+ }
+ return 0;
+}
+
/*
Local Variables:
c-basic-offset:2