Hash strings at compile time.

compile_time_hash.h

#ifndef compile_time_hash_h
#define compile_time_hash_h

// Posted by jbowes. Public domain. 
// source: (dead link)
// http://lol.zoy.org/blog/2011/12/20/cpp-constant-string-hash
// 
// At higher compiler optimization levels (-O1 and higher on clang/llvm), 
// C_HASH("string") should be replaced by a hash of "string" at compile time. 

#include <string.h>
#include <stdint.h>
 
#define H1(s,i,x)   (x * 65599u + (uint8_t)s[(i) < strlen(s) ? strlen(s) - 1 - (i) : strlen(s)])
#define H4(s,i,x)   H1(s, i, H1(s, i + 1, H1(s, i + 2, H1(s, i + 3, x))))
#define H16(s,i,x)  H4(s, i, H4(s, i + 4, H4(s, i + 8, H4(s, i + 12, x))))
#define H64(s,i,x)  H16(s, i, H16(s, i + 16, H16(s, i + 32, H16(s, i + 48, x))))
#define H256(s,i,x) H64(s, i, H64(s, i + 64, H64(s, i + 128, H64(s, i + 192, x))))

// Replace H16 if you want to handle longer strings, but you may
// run into your preprocessor's recursion limit.
// 17 is just a prime factor.
#define C_HASH(s)    ((uint32_t)(H16(s,0,31)))
 
 
#endif