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Update comments in sha.cpp

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Jeffrey Walton 2019-05-19 15:51:09 -04:00
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// sha.cpp - modified by Wei Dai from Steve Reid's public domain sha1.c // sha.cpp - modified by Wei Dai from Steve Reid's public domain sha1.c
// Steve Reid implemented SHA-1. Wei Dai implemented SHA-2. Jeffrey Walton // Steve Reid implemented SHA-1. Wei Dai implemented SHA-2. Jeffrey
// implemented Intel SHA extensions based on Intel articles and code by // Walton implemented Intel SHA extensions based on Intel articles and code
// Sean Gulley. Jeffrey Walton implemented ARM SHA based on ARM code and // by Sean Gulley. Jeffrey Walton implemented ARM SHA based on ARM code and
// code from Johannes Schneiders, Skip Hovsmith and Barry O'Rourke. // code from Johannes Schneiders, Skip Hovsmith and Barry O'Rourke. All
// All code is in the public domain. // code is in the public domain.
// In August 2017 JW reworked the internals to align all the implementations. // In August 2017 JW reworked the internals to align all the
// Formerly all hashes were software based, IterHashBase handled endian conversions, // implementations. Formerly all hashes were software based, IterHashBase
// and IterHashBase dispatched a single to block SHA{N}::Transform. SHA{N}::Transform // handled endian conversions, and IterHashBase dispatched a single to
// then performed the single block hashing. It was repeated for multiple blocks. // block SHA{N}::Transform. SHA{N}::Transform then performed the single
// block hashing. It was repeated for multiple blocks.
// //
// The rework added SHA{N}::HashMultipleBlocks (class) and SHA{N}_HashMultipleBlocks // The rework added SHA{N}::HashMultipleBlocks (class) and
// (free standing). There are also hardware accelerated variations. Callers enter // SHA{N}_HashMultipleBlocks (free standing). There are also hardware
// SHA{N}::HashMultipleBlocks (class), and the function calls SHA{N}_HashMultipleBlocks // accelerated variations. Callers enter SHA{N}::HashMultipleBlocks (class)
// (free standing) or SHA{N}_HashBlock (free standing) as a fallback. // and the function calls SHA{N}_HashMultipleBlocks (free standing) or
// SHA{N}_HashBlock (free standing) as a fallback.
// //
// An added wrinkle is hardware is little endian, C++ is big endian, and callers use // An added wrinkle is hardware is little endian, C++ is big endian, and
// big endian, so SHA{N}_HashMultipleBlock accepts a ByteOrder for the incoming data // callers use big endian, so SHA{N}_HashMultipleBlock accepts a ByteOrder
// arrangement. Hardware based SHA{N}_HashMultipleBlock can often perform the endian // for the incoming data arrangement. Hardware based SHA{N}_HashMultipleBlock
// swap much easier by setting an EPI mask. Endian swap incurs no penalty on Intel SHA, // can often perform the endian swap much easier by setting an EPI mask.
// and 4-instruction penalty on ARM SHA. Under C++ the full software based swap penalty // Endian swap incurs no penalty on Intel SHA, and 4-instruction penalty on
// is incurred due to use of ReverseBytes(). // ARM SHA. Under C++ the full software based swap penalty is incurred due
// to use of ReverseBytes().
// //
// The rework also removed the hacked-in pointers to implementations. // In May 2019 JW added Cryptogams ARMv7 and NEON implementations for SHA1,
// SHA256 and SHA512. The Cryptogams code closed a performance gap on modern
// 32-bit ARM devices. Cryptogams is Andy Polyakov's project used to create
// high speed crypto algorithms and share them with other developers. Andy's
// code runs 30% to 50% faster than C/C++ code. The Cryptogams code can be
// disabled in config_asm.h. An example of integrating Andy's code is at
// https://wiki.openssl.org/index.php/Cryptogams_SHA.
// use "cl /EP /P /DCRYPTOPP_GENERATE_X64_MASM sha.cpp" to generate MASM code // use "cl /EP /P /DCRYPTOPP_GENERATE_X64_MASM sha.cpp" to generate MASM code