Improved performance on dedicated P-256/i15 EC implementation.

src/config.h

@@ -50,6 +50,15 @@
 #define BR_SLOW_MUL   1
  */
 
+/*
+ * When BR_SLOW_MUL15 is enabled, short multplications (on 15-bit words)
+ * are assumed to be substantially slow with regards to other integer
+ * operations, thus making it worth to make more integer operations if
+ * it allows using less multiplications.
+ *
+#define BR_SLOW_MUL15   1
+ */
+
 /*
  * When BR_CT_MUL31 is enabled, multiplications of 31-bit values (used
  * in the "i31" big integer implementation) use an alternate implementation