tools/testing/selftests/bpf/progs/test_jhash.h

// SPDX-License-Identifier: GPL-2.0
// Copyright (c) 2019 Facebook
#include <features.h>

typedef unsigned int u32;

static __always_inline u32 rol32(u32 word, unsigned int shift)
{
	return (word << shift) | (word >> ((-shift) & 31));
}

#define __jhash_mix(a, b, c)			\
{						\
	a -= c;  a ^= rol32(c, 4);  c += b;	\
	b -= a;  b ^= rol32(a, 6);  a += c;	\
	c -= b;  c ^= rol32(b, 8);  b += a;	\
	a -= c;  a ^= rol32(c, 16); c += b;	\
	b -= a;  b ^= rol32(a, 19); a += c;	\
	c -= b;  c ^= rol32(b, 4);  b += a;	\
}

#define __jhash_final(a, b, c)			\
{						\
	c ^= b; c -= rol32(b, 14);		\
	a ^= c; a -= rol32(c, 11);		\
	b ^= a; b -= rol32(a, 25);		\
	c ^= b; c -= rol32(b, 16);		\
	a ^= c; a -= rol32(c, 4);		\
	b ^= a; b -= rol32(a, 14);		\
	c ^= b; c -= rol32(b, 24);		\
}

#define JHASH_INITVAL		0xdeadbeef

static ATTR
u32 jhash(const void *key, u32 length, u32 initval)
{
	u32 a, b, c;
	const unsigned char *k = key;

	a = b = c = JHASH_INITVAL + length + initval;

	while (length > 12) {
		a += *(volatile u32 *)(k);
		b += *(volatile u32 *)(k + 4);
		c += *(volatile u32 *)(k + 8);
		__jhash_mix(a, b, c);
		length -= 12;
		k += 12;
	}
	switch (length) {
	case 12: c += (u32)k[11]<<24;
	case 11: c += (u32)k[10]<<16;
	case 10: c += (u32)k[9]<<8;
	case 9:  c += k[8];
	case 8:  b += (u32)k[7]<<24;
	case 7:  b += (u32)k[6]<<16;
	case 6:  b += (u32)k[5]<<8;
	case 5:  b += k[4];
	case 4:  a += (u32)k[3]<<24;
	case 3:  a += (u32)k[2]<<16;
	case 2:  a += (u32)k[1]<<8;
	case 1:  a += k[0];
		 c ^= a;
		 __jhash_final(a, b, c);
	case 0: /* Nothing left to add */
		break;
	}

	return c;
}