add comparison function

bigint.h

@@ -146,6 +146,9 @@ int bigint_from_cstring(bigint* b, const char* str, unsigned int base);
 BIGINT_API
 size_t bigint_to_string(char* str, size_t len, const bigint* b, unsigned int base);
 
+BIGINT_API
+int bigint_cmp(const bigint *a, const bigint *b);
+
 BIGINT_API
 int bigint_inc(bigint* c, const bigint *a);
 
@@ -164,13 +167,6 @@ int bigint_mul(bigint* c, const bigint* a, const bigint* b);
 BIGINT_API
 int bigint_div_mod(bigint* quotient, bigint* remainder, const bigint* numerator, const bigint* denominator);
 
-/* faster div_mod for when you're dividing by a regular, positive word type - note that this
- * overwrites numerator! roughly equivalent to:
- * remainder = numerator % denominator
- * numerator /= denominator */
-BIGINT_API
-void bigint_div_mod_word(bigint* numerator, bigint_word* remainder, bigint_word denominator);
-
 BIGINT_API
 int bigint_lshift(bigint* c, const bigint* a, size_t bits);
 
@@ -183,6 +179,13 @@ int bigint_lshift_overwrite(bigint* a, size_t bits);
 BIGINT_API
 int bigint_rshift_overwrite(bigint* a, size_t bits);
 
+/* faster div_mod for when you're dividing by a regular, positive word type - note that this
+ * overwrites numerator! roughly equivalent to:
+ * remainder = numerator % denominator
+ * numerator /= denominator */
+BIGINT_API
+void bigint_div_mod_word(bigint* numerator, bigint_word* remainder, bigint_word denominator);
+
 #ifdef __cplusplus
 }
 #endif
@@ -1623,4 +1626,12 @@ size_t bigint_to_string(char* str, size_t len, const bigint* b, unsigned int bas
     return res;
 }
 
+BIGINT_API
+int bigint_cmp(const bigint *a, const bigint *b) {
+    if(!a->size && !b->size) return 0;
+    if(a->sign && b->sign) return bigint_cmp_abs(b,a);
+    if(a->sign == b->sign) return bigint_cmp_abs(a,b);
+    return a->sign && !b->sign ? -1 : 1;
+}
+
 #endif