Ignore .so

.clang-format

@@ -15,3 +15,4 @@ AlignConsecutiveDeclarations:
   AlignFunctionPointers: false
   PadOperators:    false
 AlignConsecutiveMacros: true
+AllowShortCaseLabelsOnASingleLine: true

.gitignore

@@ -1,4 +1,5 @@
 *.o
+*.so
 .cache
 .json
 *.elf

lookup3.c

@@ -0,0 +1,63 @@
+#include <stdint.h>
+#include <stdlib.h>
+
+#define rot(x, k) (((x) << (k)) | ((x) >> (32 - (k))))
+
+// clang-format off
+#define mix(a,b,c) \
+{ \
+  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; \
+}
+
+#define final(a,b,c) \
+{ \
+  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); \
+}
+// clang-format on
+
+uint32_t lookup3(const void *key, size_t length, uint32_t initval) {
+    uint32_t        a, b, c;
+    const uint8_t  *k;
+    const uint32_t *data32Bit;
+
+    data32Bit = key;
+    a = b = c = 0xdeadbeef + (((uint32_t)length) << 2) + initval;
+
+    while (length > 12) {
+        a += *(data32Bit++);
+        b += *(data32Bit++);
+        c += *(data32Bit++);
+        mix(a, b, c);
+        length -= 12;
+    }
+
+    k = (const uint8_t *)data32Bit;
+    switch (length) {
+    case 12: c += ((uint32_t)k[11]) << 24;
+    case 11: c += ((uint32_t)k[10]) << 16;
+    case 10: c += ((uint32_t)k[9]) << 8;
+    case 9: c += k[8];
+    case 8: b += ((uint32_t)k[7]) << 24;
+    case 7: b += ((uint32_t)k[6]) << 16;
+    case 6: b += ((uint32_t)k[5]) << 8;
+    case 5: b += k[4];
+    case 4: a += ((uint32_t)k[3]) << 24;
+    case 3: a += ((uint32_t)k[2]) << 16;
+    case 2: a += ((uint32_t)k[1]) << 8;
+    case 1: a += k[0]; break;
+    case 0: return c;
+    }
+    final(a, b, c);
+    return c;
+}

lua_lib/Makefile

@@ -0,0 +1,21 @@
+CC      ?= gcc
+CFLAGS  ?= -Wall -O2 -fPIC
+LDFLAGS ?=
+
+TARGET  = lookup3.so
+SRC     = lua_lookup3.c
+OBJS    = lua_lookup3.o lookup3.o
+
+all: $(TARGET)
+
+$(TARGET): $(OBJS)
+	$(CC) -shared -o $@ $^ $(LDFLAGS)
+
+lua_lookup3.o: $(SRC)
+	$(CC) $(CFLAGS) -c -o $@ $<
+
+lookup3.o: ../lookup3.c
+	$(CC) $(CFLAGS) -c -o $@ $<
+
+clean:
+	rm -f $(TARGET) $(OBJS)

lua_lib/driver.lua

@@ -0,0 +1,2 @@
+local myhash = require "lookup3"
+print(myhash.lookup3("hello", 0) % 100)

lua_lib/lua_lookup3.c

@@ -0,0 +1,27 @@
+#include <lua.h>
+#include <lauxlib.h>
+#include <stdint.h>
+
+uint32_t lookup3(const void *key, size_t length, uint32_t initval);
+
+// Lua wrapper
+static int l_lookup3(lua_State *L) {
+    size_t len;
+    const char *str = luaL_checklstring(L, 1, &len);  // get string + length
+    uint32_t initval = (uint32_t)luaL_checkinteger(L, 2); // get initval
+
+    uint32_t hash = lookup3(str, len, initval);
+
+    lua_pushinteger(L, hash);  // return the hash
+    return 1;                  // number of return values
+}
+
+// Module open function
+int luaopen_lookup3(lua_State *L) {
+    lua_newtable(L);
+
+    lua_pushcfunction(L, l_lookup3);
+    lua_setfield(L, -2, "lookup3");
+
+    return 1;  // return the table
+}