add BAFH: Better Avalanche for the Jenkins hash
This uses NZAAT Init and Update, and AES MixColumns for Finish. For hashtables this will need XOR with uint32_t then rotation with uint5_t (so a total of 37 bit of entropy) for mitigation. For entropy avalanche this needs mixing, and better handling of the IV and/or the first four bytes, see BAFHHost* macros. Thanks to Bob Jenkins for the one-at-a-time hash, Bret Mulvey for the Hash.cs AvalancheTest, Jonathan “ciruZ” Schleifer and Dominik “Natureshadow” George for discussion, Theodore “Ted” Ts'o for valuable input on arc4random_roundhash, “poncho” for suggesting and Orson “nightcracker” Peters for implementing MixColumns, tarent GmbH for letting me test this empirically on a 64 GiB RAM machine.
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mirhash.h
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mirhash.h
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/*-
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* Copyright © 2011, 2014
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* Thorsten Glaser <tg@mirbsd.org>
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*
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* Provided that these terms and disclaimer and all copyright notices
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* are retained or reproduced in an accompanying document, permission
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* is granted to deal in this work without restriction, including un‐
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* limited rights to use, publicly perform, distribute, sell, modify,
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* merge, give away, or sublicence.
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*
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* This work is provided “AS IS” and WITHOUT WARRANTY of any kind, to
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* the utmost extent permitted by applicable law, neither express nor
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* implied; without malicious intent or gross negligence. In no event
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* may a licensor, author or contributor be held liable for indirect,
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* direct, other damage, loss, or other issues arising in any way out
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* of dealing in the work, even if advised of the possibility of such
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* damage or existence of a defect, except proven that it results out
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* of said person’s immediate fault when using the work as intended.
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*-
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* This file provides BAFH (Better Avalanche for the Jenkins Hash) as
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* inline macro bodies that operate on “register uint32_t” variables,
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* with variants that use their local intermediate registers.
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*
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* Usage note for BAFH with entropy distribution: input up to 4 bytes
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* is best combined into a 32-bit unsigned integer, which is then run
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* through BAFHFinish_reg for mixing and then used as context instead
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* of 0. Longer input should be handled the same: take the first four
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* bytes as IV after mixing then add subsequent bytes the same way.
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* This needs counting input bytes and is endian-dependent, thus not,
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* for speed reasons, specified for the regular stable hash, but very
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* much recommended if the actual output value may differ across runs
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* (so is using a random value instead of 0 for the IV).
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*/
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#ifndef SYSKERN_MIRHASH_H
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#define SYSKERN_MIRHASH_H 1
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#define SYSKERN_MIRHASH_BAFH
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#include <sys/types.h>
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__RCSID("$MirOS: src/bin/mksh/mirhash.h,v 1.1 2014/01/11 15:59:41 tg Exp $");
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/*-
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* BAFH itself is defined by the following primitives:
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*
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* • BAFHInit(ctx) initialises the hash context, which consists of a
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* sole 32-bit unsigned integer (ideally in a register), to 0.
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* It is possible to use any initial value out of [0; 2³²[ – which
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* is, in fact, recommended if using BAFH for entropy distribution
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* – but for a regular stable hash, the IV 0 is needed.
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*
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* • BAFHUpdateOctet(ctx,val) compresses the unsigned 8-bit quantity
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* into the hash context. The algorithm used is Jenkins’ one-at-a-
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* time, except that an additional constant 1 is added so that, if
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* the context is (still) zero, adding a NUL byte is not ignored.
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*
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* • BAFHror(eax,cl) evaluates to the unsigned 32-bit integer “eax”,
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* rotated right by “cl” ∈ [0;31]; no casting, be careful!
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*
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* • BAFHFinish(ctx) avalanches the context around so every sub-byte
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* depends on all input octets; afterwards, the context variable’s
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* value is the hash output. BAFH does not use any padding, nor is
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* the input length added; this is due to the common use case (for
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* quick entropy distribution and use with a hashtable).
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* Warning: BAFHFinish uses the MixColumn algorithm of AES – which
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* is reversible (to avoid introducing funnels and reducing entro‐
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* py), so blinding may need to be employed for some uses, e.g. in
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* mksh, after a fork.
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*
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* The BAFHUpdateOctet and BAFHFinish are available in two flavours:
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* suffixed with _reg (assumes the context is in a register) or _mem
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* (which doesn’t).
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*
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* The following high-level macros (with _reg and _mem variants) are
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* available:
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*
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* • BAFHUpdateMem(ctx,buf,len) adds a memory block to a context.
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* • BAFHUpdateStr(ctx,buf) is equivalent to using len=strlen(buf).
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* • BAFHHostMem(ctx,buf,len) calculates the hash of the memory buf‐
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* fer using the first 4 octets (mixed) for IV, as outlined above;
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* the result is endian-dependent; “ctx” assumed to be a register.
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* • BAFHHostStr(ctx,buf) does the same for C strings.
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*
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* All macros may use ctx multiple times in their expansion, but all
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* other arguments are always evaluated at most once.
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*/
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#define BAFHInit(h) do { \
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(h) = 0; \
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} while (/* CONSTCOND */ 0)
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#define BAFHUpdateOctet_reg(h,b) do { \
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(h) += (uint8_t)(b); \
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++(h); \
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(h) += (h) << 10; \
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(h) ^= (h) >> 6; \
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} while (/* CONSTCOND */ 0)
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#define BAFHUpdateOctet_mem(m,b) do { \
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register uint32_t BAFH_h = (m); \
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\
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BAFHUpdateOctet_reg(BAFH_h, (b)); \
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(m) = BAFH_h; \
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} while (/* CONSTCOND */ 0)
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#define BAFHror(eax,cl) (((eax) >> (cl)) | ((eax) << (32 - (cl))))
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#define BAFHFinish_reg(h) do { \
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register uint32_t BAFHFinish_v; \
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\
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BAFHFinish_v = ((h) >> 7) & 0x01010101U; \
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BAFHFinish_v += BAFHFinish_v << 1; \
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BAFHFinish_v += BAFHFinish_v << 3; \
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BAFHFinish_v ^= ((h) << 1) & 0xFEFEFEFEU; \
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\
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BAFHFinish_v ^= BAFHror(BAFHFinish_v, 8); \
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BAFHFinish_v ^= ((h) = BAFHror((h), 8)); \
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BAFHFinish_v ^= ((h) = BAFHror((h), 8)); \
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(h) = BAFHror((h), 8) ^ BAFHFinish_v; \
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} while (/* CONSTCOND */ 0)
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#define BAFHFinish_mem(m) do { \
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register uint32_t BAFHFinish_v, BAFH_h = (m); \
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\
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BAFHFinish_v = (BAFH_h >> 7) & 0x01010101U; \
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BAFHFinish_v += BAFHFinish_v << 1; \
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BAFHFinish_v += BAFHFinish_v << 3; \
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BAFHFinish_v ^= (BAFH_h << 1) & 0xFEFEFEFEU; \
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\
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BAFHFinish_v ^= BAFHror(BAFHFinish_v, 8); \
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BAFHFinish_v ^= (BAFH_h = BAFHror(BAFH_h, 8)); \
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BAFHFinish_v ^= (BAFH_h = BAFHror(BAFH_h, 8)); \
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(m) = BAFHror(BAFH_h, 8) ^ BAFHFinish_v; \
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} while (/* CONSTCOND */ 0)
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#define BAFHUpdateMem_reg(h,p,z) do { \
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register const uint8_t *BAFHUpdate_p; \
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register size_t BAFHUpdate_z = (z); \
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\
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BAFHUpdate_p = (const void *)(p); \
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while (BAFHUpdate_z--) \
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BAFHUpdateOctet_reg((h), *BAFHUpdate_p++); \
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} while (/* CONSTCOND */ 0)
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/* meh should have named them _r/m but that’s not valid C */
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#define BAFHUpdateMem_mem(m,p,z) do { \
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register uint32_t BAFH_h = (m); \
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\
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BAFHUpdateMem_reg(BAFH_h, (p), (z)); \
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(m) = BAFH_h; \
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} while (/* CONSTCOND */ 0)
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#define BAFHUpdateStr_reg(h,s) do { \
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register const uint8_t *BAFHUpdate_s; \
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register uint8_t BAFHUpdate_c; \
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\
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BAFHUpdate_s = (const void *)(s); \
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while ((BAFHUpdate_c = *BAFHUpdate_s++) != 0) \
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BAFHUpdateOctet_reg((h), BAFHUpdate_c); \
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} while (/* CONSTCOND */ 0)
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#define BAFHUpdateStr_mem(m,s) do { \
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register uint32_t BAFH_h = (m); \
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\
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BAFHUpdateStr_reg(BAFH_h, (s)); \
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(m) = BAFH_h; \
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} while (/* CONSTCOND */ 0)
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#define BAFHHostMem(h,p,z) do { \
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register const uint8_t *BAFHUpdate_p; \
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register size_t BAFHUpdate_z = (z); \
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size_t BAFHHost_z; \
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union { \
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uint8_t as_u8[4]; \
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uint32_t as_u32; \
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} BAFHHost_v; \
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\
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BAFHUpdate_p = (const void *)(p); \
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BAFHHost_v.as_u32 = 0; \
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BAFHHost_z = BAFHUpdate_z < 4 ? BAFHUpdate_z : 4; \
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memcpy(BAFHHost_v.as_u8, BAFHUpdate_p, BAFHHost_z); \
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BAFHUpdate_p += BAFHHost_z; \
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BAFHUpdate_z -= BAFHHost_z; \
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(h) = BAFHHost_v.as_u32; \
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BAFHFinish_reg(h); \
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while (BAFHUpdate_z--) \
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BAFHUpdateOctet_reg((h), *BAFHUpdate_p++); \
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BAFHFinish_reg(h); \
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} while (/* CONSTCOND */ 0)
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#define BAFHHostStr(h,s) do { \
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register const uint8_t *BAFHUpdate_s; \
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register uint8_t BAFHUpdate_c; \
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union { \
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uint8_t as_u8[4]; \
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uint32_t as_u32; \
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} BAFHHost_v; \
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\
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BAFHUpdate_s = (const void *)(s); \
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if ((BAFHHost_v.as_u8[0] = *BAFHUpdate_s) != 0) \
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++BAFHUpdate_s; \
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if ((BAFHHost_v.as_u8[1] = *BAFHUpdate_s) != 0) \
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++BAFHUpdate_s; \
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if ((BAFHHost_v.as_u8[2] = *BAFHUpdate_s) != 0) \
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++BAFHUpdate_s; \
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if ((BAFHHost_v.as_u8[3] = *BAFHUpdate_s) != 0) \
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++BAFHUpdate_s; \
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(h) = BAFHHost_v.as_u32; \
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BAFHFinish_reg(h); \
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while ((BAFHUpdate_c = *BAFHUpdate_s++) != 0) \
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BAFHUpdateOctet_reg((h), BAFHUpdate_c); \
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BAFHFinish_reg(h); \
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} while (/* CONSTCOND */ 0)
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#endif
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