feat: Add Jenkins Lookup3 hash function

hash/README.md

@@ -6,3 +6,4 @@
 * adler_32 (32 bit)
 * crc32 (32 bit)
 * BLAKE2b
+* Lookup3 (32 bit)

hash/hash_lookup3.c

@@ -0,0 +1,106 @@
+/**
+ * @addtogroup hash Hash algorithms
+ * @{
+ * @file hash_lookup3.c
+ * @author [cptr0](https://github.com/cptr0)
+ * @brief 32-bit [Jenkins hash](https://en.wikipedia.org/wiki/Jenkins_hash_function) algorithm
+ */
+
+#include <assert.h>
+#include <inttypes.h>
+#include <string.h>
+#include <stdio.h>
+
+// Rotate x left by k bits
+#define rot(x,k) (((x) << (k)) | ((x) >> (32-(k))))
+
+/**
+ * @brief 32-bit Jenkins Lookup3 algorithm implementation
+ *
+ * @param s NULL terminated ASCII string to hash
+ * @return 32-bit hash result
+ */
+
+uint32_t lookup3_32(const char *key, uint32_t seed) 
+{
+    uint32_t a, b, c;
+    a = b = 0x9e3779b9;
+    c = seed;
+
+    size_t i = 0;
+
+    size_t length = strlen(key);
+
+    while (length - i >= 12) 
+    {
+        a += (uint32_t)key[i] | ((uint32_t)key[i+1] << 8) |
+             ((uint32_t)key[i+2] << 16) | ((uint32_t)key[i+3] << 24);
+        b += (uint32_t)key[i+4] | ((uint32_t)key[i+5] << 8) |
+             ((uint32_t)key[i+6] << 16) | ((uint32_t)key[i+7] << 24);
+        c += (uint32_t)key[i+8] | ((uint32_t)key[i+9] << 8) |
+             ((uint32_t)key[i+10] << 16) | ((uint32_t)key[i+11] << 24);
+
+        a -= c;  a ^= rot(c,4);  c += b;
+        b -= a;  b ^= rot(a,6);  a += c;
+        c -= b;  c ^= rot(b,8);  b += a;
+        a -= c;  a ^= rot(c,16); c += b;
+        b -= a;  b ^= rot(a,19); a += c;
+        c -= b;  c ^= rot(b,4);  b += a;
+
+        i += 12;
+    }
+
+    uint32_t remainingA = 0, remainingB = 0, remainingC = 0;
+    switch (length - i) 
+    {
+        case 11: remainingC += ((uint32_t)key[i+10]) << 16;
+        case 10: remainingC += ((uint32_t)key[i+9]) << 8;
+        case 9:  remainingC += (uint32_t)key[i+8];
+        case 8:  remainingB += ((uint32_t)key[i+7]) << 24;
+        case 7:  remainingB += ((uint32_t)key[i+6]) << 16;
+        case 6:  remainingB += ((uint32_t)key[i+5]) << 8;
+        case 5:  remainingB += (uint32_t)key[i+4];
+        case 4:  remainingA += ((uint32_t)key[i+3]) << 24;
+        case 3:  remainingA += ((uint32_t)key[i+2]) << 16;
+        case 2:  remainingA += ((uint32_t)key[i+1]) << 8;
+        case 1:  remainingA += (uint32_t)key[i];
+                 a += remainingA;
+                 b += remainingB;
+                 c += remainingC;
+    }
+
+    c ^= b; c -= rot(b,14);
+    a ^= c; a -= rot(c,11);
+    b ^= a; b -= rot(a,25);
+    c ^= b; c -= rot(b,16);
+    a ^= c; a -= rot(c,4);
+    b ^= a; b -= rot(a,14);
+    c ^= b; c -= rot(b,24);
+
+    return c;
+}
+/**
+ * @brief Test function for lookup3_32 function
+ *
+ * @returns None
+ */
+void test_lookup3_32()
+{
+    assert(lookup3_32("Hello, Jenkins!", 0) == 2484708164);
+    assert(lookup3_32("Hello Jenkinss", 0) == 850494015);
+    assert(lookup3_32("Hello, Jenkins", 0) == 3393305742);
+    assert(lookup3_32("hello, jenkins!", 0) == 3521406038);
+
+    printf("%s", "Test passed.\n");
+}
+
+/**
+ * @brief Main function
+ *
+ * @returns 0 on successful program exit
+ */
+int main()
+{
+    test_lookup3_32();
+    return 0;
+}