Allow disabling keyed hash function (prf) in conf

In some cases, one might want to disable what is currently
SipHash for speed / better security mechansims. For example, using
red black trees for caches rather than hash tables.

src/conf/janetconf.h

@@ -51,6 +51,7 @@
 /* #define JANET_NO_PEG */
 /* #define JANET_NO_TYPED_ARRAY */
 /* #define JANET_NO_INT_TYPES */
+/* #define JANET_NO_PRF */
 /* #define JANET_OUT_OF_MEMORY do { printf("janet out of memory\n"); exit(1); } while (0) */
 /* #define JANET_RECURSION_GUARD 1024 */
 /* #define JANET_MAX_PROTO_DEPTH 200 */

src/core/util.c

@@ -94,6 +94,18 @@ const char *const janet_status_names[16] = {
     "alive"
 };
 
+#ifdef JANET_NO_PRF
+
+int32_t janet_string_calchash(const uint8_t *str, int32_t len) {
+    const uint8_t *end = str + len;
+    uint32_t hash = 5381;
+    while (str < end)
+        hash = (hash << 5) + hash + *str++;
+    return (int32_t) hash;
+}
+
+#else
+
 /*
   Public domain siphash implementation sourced from:
 
@@ -202,6 +214,8 @@ int32_t janet_string_calchash(const uint8_t *str, int32_t len) {
     return (int32_t)hash;
 }
 
+#endif
+
 /* Computes hash of an array of values */
 int32_t janet_array_calchash(const Janet *array, int32_t len) {
     const Janet *end = array + len;

src/include/janet.h

@@ -1302,8 +1302,10 @@ JANET_API int janet_verify(JanetFuncDef *def);
 JANET_API JanetBuffer *janet_pretty(JanetBuffer *buffer, int depth, int flags, Janet x);
 
 /* Misc */
-JANET_API int janet_equals(Janet x, Janet y);
+#ifndef JANET_NO_PRF
 JANET_API void janet_init_hash_key(uint8_t key[16]);
+#endif
+JANET_API int janet_equals(Janet x, Janet y);
 JANET_API int32_t janet_hash(Janet x);
 JANET_API int janet_compare(Janet x, Janet y);
 JANET_API int janet_cstrcmp(JanetString str, const char *other);