mksh/mirhash.h

/*-
 * Copyright © 2011, 2014, 2015
 *	Thorsten “mirabilos” Glaser <tg@mirbsd.org>
 *
 * Provided that these terms and disclaimer and all copyright notices
 * are retained or reproduced in an accompanying document, permission
 * is granted to deal in this work without restriction, including un‐
 * limited rights to use, publicly perform, distribute, sell, modify,
 * merge, give away, or sublicence.
 *
 * This work is provided “AS IS” and WITHOUT WARRANTY of any kind, to
 * the utmost extent permitted by applicable law, neither express nor
 * implied; without malicious intent or gross negligence. In no event
 * may a licensor, author or contributor be held liable for indirect,
 * direct, other damage, loss, or other issues arising in any way out
 * of dealing in the work, even if advised of the possibility of such
 * damage or existence of a defect, except proven that it results out
 * of said person’s immediate fault when using the work as intended.
 *-
 * This file provides BAFH (Better Avalanche for the Jenkins Hash) as
 * inline macro bodies that operate on “register uint32_t” variables,
 * with variants that use their local intermediate registers.
 *
 * Usage note for BAFH with entropy distribution: input up to 4 bytes
 * is best combined into a 32-bit unsigned integer, which is then run
 * through BAFHFinish_reg for mixing and then used as context instead
 * of 0. Longer input should be handled the same: take the first four
 * bytes as IV after mixing then add subsequent bytes the same way.
 * This needs counting input bytes and is endian-dependent, thus not,
 * for speed reasons, specified for the regular stable hash, but very
 * much recommended if the actual output value may differ across runs
 * (so is using a random value instead of 0 for the IV).
 *-
 * Little quote gem:
 *	We are looking into it. Changing the core
 *	hash function in PHP isn't a trivial change
 *	and will take us some time.
 * -- Rasmus Lerdorf
 */

#ifndef SYSKERN_MIRHASH_H
#define SYSKERN_MIRHASH_H 1
#define SYSKERN_MIRHASH_BAFH

#include <sys/types.h>

__RCSID("$MirOS: src/bin/mksh/mirhash.h,v 1.4 2015/05/30 22:14:06 tg Exp $");

/*-
 * BAFH itself is defined by the following primitives:
 *
 * • BAFHInit(ctx) initialises the hash context, which consists of a
 *   sole 32-bit unsigned integer (ideally in a register), to 0.
 *   It is possible to use any initial value out of [0; 2³²[ – which
 *   is, in fact, recommended if using BAFH for entropy distribution
 *   – but for a regular stable hash, the IV 0 is needed.
 *
 * • BAFHUpdateOctet(ctx,val) compresses the unsigned 8-bit quantity
 *   into the hash context. The algorithm used is Jenkins’ one-at-a-
 *   time, except that an additional constant 1 is added so that, if
 *   the context is (still) zero, adding a NUL byte is not ignored.
 *
 * • BAFHror(eax,cl) evaluates to the unsigned 32-bit integer “eax”,
 *   rotated right by “cl” ∈ [0; 31] (no casting, be careful!) where
 *   “eax” must be uint32_t and “cl” an in-range integer.
 *
 * • BAFHFinish(ctx) avalanches the context around so every sub-byte
 *   depends on all input octets; afterwards, the context variable’s
 *   value is the hash output. BAFH does not use any padding, nor is
 *   the input length added; this is due to the common use case (for
 *   quick entropy distribution and use with a hashtable).
 *   Warning: BAFHFinish uses the MixColumn algorithm of AES – which
 *   is reversible (to avoid introducing funnels and reducing entro‐
 *   py), so blinding may need to be employed for some uses, e.g. in
 *   mksh, after a fork.
 *
 * The BAFHUpdateOctet and BAFHFinish are available in two flavours:
 * suffixed with _reg (assumes the context is in a register) or _mem
 * (which doesn’t).
 *
 * The following high-level macros (with _reg and _mem variants) are
 * available:
 *
 * • BAFHUpdateMem(ctx,buf,len) adds a memory block to a context.
 * • BAFHUpdateStr(ctx,buf) is equivalent to using len=strlen(buf).
 * • BAFHHostMem(ctx,buf,len) calculates the hash of the memory buf‐
 *   fer using the first 4 octets (mixed) for IV, as outlined above;
 *   the result is endian-dependent; “ctx” assumed to be a register.
 * • BAFHHostStr(ctx,buf) does the same for C strings.
 *
 * All macros may use ctx multiple times in their expansion, but all
 * other arguments are always evaluated at most once except BAFHror.
 *
 * To stay portable, never use the BAFHHost*() macros (these are for
 * host-local entropy shuffling), and encode numbers using ULEB128.
 */

#define BAFHInit(h) do {					\
	(h) = 0;						\
} while (/* CONSTCOND */ 0)

#define BAFHUpdateOctet_reg(h,b) do {				\
	(h) += (uint8_t)(b);					\
	++(h);							\
	(h) += (h) << 10;					\
	(h) ^= (h) >> 6;					\
} while (/* CONSTCOND */ 0)

#define BAFHUpdateOctet_mem(m,b) do {				\
	register uint32_t BAFH_h = (m);				\
								\
	BAFHUpdateOctet_reg(BAFH_h, (b));			\
	(m) = BAFH_h;						\
} while (/* CONSTCOND */ 0)

#define BAFHror(eax,cl) (((eax) >> (cl)) | ((eax) << (32 - (cl))))

#define BAFHFinish_reg(h) do {					\
	register uint32_t BAFHFinish_v;				\
								\
	BAFHFinish_v = ((h) >> 7) & 0x01010101U;		\
	BAFHFinish_v += BAFHFinish_v << 1;			\
	BAFHFinish_v += BAFHFinish_v << 3;			\
	BAFHFinish_v ^= ((h) << 1) & 0xFEFEFEFEU;		\
								\
	BAFHFinish_v ^= BAFHror(BAFHFinish_v, 8);		\
	BAFHFinish_v ^= ((h) = BAFHror((h), 8));		\
	BAFHFinish_v ^= ((h) = BAFHror((h), 8));		\
	(h) = BAFHror((h), 8) ^ BAFHFinish_v;			\
} while (/* CONSTCOND */ 0)

#define BAFHFinish_mem(m) do {					\
	register uint32_t BAFHFinish_v, BAFH_h = (m);		\
								\
	BAFHFinish_v = (BAFH_h >> 7) & 0x01010101U;		\
	BAFHFinish_v += BAFHFinish_v << 1;			\
	BAFHFinish_v += BAFHFinish_v << 3;			\
	BAFHFinish_v ^= (BAFH_h << 1) & 0xFEFEFEFEU;		\
								\
	BAFHFinish_v ^= BAFHror(BAFHFinish_v, 8);		\
	BAFHFinish_v ^= (BAFH_h = BAFHror(BAFH_h, 8));		\
	BAFHFinish_v ^= (BAFH_h = BAFHror(BAFH_h, 8));		\
	(m) = BAFHror(BAFH_h, 8) ^ BAFHFinish_v;		\
} while (/* CONSTCOND */ 0)

#define BAFHUpdateMem_reg(h,p,z) do {				\
	register const uint8_t *BAFHUpdate_p;			\
	register size_t BAFHUpdate_z = (z);			\
								\
	BAFHUpdate_p = (const void *)(p);			\
	while (BAFHUpdate_z--)					\
		BAFHUpdateOctet_reg((h), *BAFHUpdate_p++);	\
} while (/* CONSTCOND */ 0)

/* meh should have named them _r/m but that’s not valid C */
#define BAFHUpdateMem_mem(m,p,z) do {				\
	register uint32_t BAFH_h = (m);				\
								\
	BAFHUpdateMem_reg(BAFH_h, (p), (z));			\
	(m) = BAFH_h;						\
} while (/* CONSTCOND */ 0)

#define BAFHUpdateStr_reg(h,s) do {				\
	register const uint8_t *BAFHUpdate_s;			\
	register uint8_t BAFHUpdate_c;				\
								\
	BAFHUpdate_s = (const void *)(s);			\
	while ((BAFHUpdate_c = *BAFHUpdate_s++) != 0)		\
		BAFHUpdateOctet_reg((h), BAFHUpdate_c);		\
} while (/* CONSTCOND */ 0)

#define BAFHUpdateStr_mem(m,s) do {				\
	register uint32_t BAFH_h = (m);				\
								\
	BAFHUpdateStr_reg(BAFH_h, (s));				\
	(m) = BAFH_h;						\
} while (/* CONSTCOND */ 0)

#define BAFHHostMem(h,p,z) do {					\
	register const uint8_t *BAFHUpdate_p;			\
	register size_t BAFHUpdate_z = (z);			\
	size_t BAFHHost_z;					\
	union {							\
		uint8_t as_u8[4];				\
		uint32_t as_u32;				\
	} BAFHHost_v;						\
								\
	BAFHUpdate_p = (const void *)(p);			\
	BAFHHost_v.as_u32 = 0;					\
	BAFHHost_z = BAFHUpdate_z < 4 ? BAFHUpdate_z : 4;	\
	memcpy(BAFHHost_v.as_u8, BAFHUpdate_p, BAFHHost_z);	\
	BAFHUpdate_p += BAFHHost_z;				\
	BAFHUpdate_z -= BAFHHost_z;				\
	(h) = BAFHHost_v.as_u32;				\
	BAFHFinish_reg(h);					\
	while (BAFHUpdate_z--)					\
		BAFHUpdateOctet_reg((h), *BAFHUpdate_p++);	\
	BAFHFinish_reg(h);					\
} while (/* CONSTCOND */ 0)

#define BAFHHostStr(h,s) do {					\
	register const uint8_t *BAFHUpdate_s;			\
	register uint8_t BAFHUpdate_c;				\
	union {							\
		uint8_t as_u8[4];				\
		uint32_t as_u32;				\
	} BAFHHost_v;						\
								\
	BAFHUpdate_s = (const void *)(s);			\
	BAFHHost_v.as_u32 = 0;					\
	if ((BAFHHost_v.as_u8[0] = *BAFHUpdate_s) != 0)		\
		++BAFHUpdate_s;					\
	if ((BAFHHost_v.as_u8[1] = *BAFHUpdate_s) != 0)		\
		++BAFHUpdate_s;					\
	if ((BAFHHost_v.as_u8[2] = *BAFHUpdate_s) != 0)		\
		++BAFHUpdate_s;					\
	if ((BAFHHost_v.as_u8[3] = *BAFHUpdate_s) != 0)		\
		++BAFHUpdate_s;					\
	(h) = BAFHHost_v.as_u32;				\
	BAFHFinish_reg(h);					\
	while ((BAFHUpdate_c = *BAFHUpdate_s++) != 0)		\
		BAFHUpdateOctet_reg((h), BAFHUpdate_c);		\
	BAFHFinish_reg(h);					\
} while (/* CONSTCOND */ 0)

#endif