abseil-cpp/absl/random/internal/randen_slow.cc

// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "absl/random/internal/randen_slow.h"

#include <cstddef>
#include <cstdint>
#include <cstring>

#include "absl/base/attributes.h"
#include "absl/base/internal/endian.h"
#include "absl/numeric/int128.h"
#include "absl/random/internal/platform.h"
#include "absl/random/internal/randen_traits.h"

#if ABSL_HAVE_ATTRIBUTE(always_inline) || \
    (defined(__GNUC__) && !defined(__clang__))
#define ABSL_RANDOM_INTERNAL_ATTRIBUTE_ALWAYS_INLINE \
  __attribute__((always_inline))
#elif defined(_MSC_VER)
// We can achieve something similar to attribute((always_inline)) with MSVC by
// using the __forceinline keyword, however this is not perfect. MSVC is
// much less aggressive about inlining, and even with the __forceinline keyword.
#define ABSL_RANDOM_INTERNAL_ATTRIBUTE_ALWAYS_INLINE __forceinline
#else
#define ABSL_RANDOM_INTERNAL_ATTRIBUTE_ALWAYS_INLINE
#endif

namespace {

// AES portions based on rijndael-alg-fst.c,
// https://fastcrypto.org/front/misc/rijndael-alg-fst.c, and modified for
// platform-endianness.
//
// Implementation of
// http://www.csrc.nist.gov/publications/fips/fips197/fips-197.pdf
constexpr uint32_t te0[256] = {
    0xa56363c6, 0x847c7cf8, 0x997777ee, 0x8d7b7bf6, 0x0df2f2ff, 0xbd6b6bd6,
    0xb16f6fde, 0x54c5c591, 0x50303060, 0x03010102, 0xa96767ce, 0x7d2b2b56,
    0x19fefee7, 0x62d7d7b5, 0xe6abab4d, 0x9a7676ec, 0x45caca8f, 0x9d82821f,
    0x40c9c989, 0x877d7dfa, 0x15fafaef, 0xeb5959b2, 0xc947478e, 0x0bf0f0fb,
    0xecadad41, 0x67d4d4b3, 0xfda2a25f, 0xeaafaf45, 0xbf9c9c23, 0xf7a4a453,
    0x967272e4, 0x5bc0c09b, 0xc2b7b775, 0x1cfdfde1, 0xae93933d, 0x6a26264c,
    0x5a36366c, 0x413f3f7e, 0x02f7f7f5, 0x4fcccc83, 0x5c343468, 0xf4a5a551,
    0x34e5e5d1, 0x08f1f1f9, 0x937171e2, 0x73d8d8ab, 0x53313162, 0x3f15152a,
    0x0c040408, 0x52c7c795, 0x65232346, 0x5ec3c39d, 0x28181830, 0xa1969637,
    0x0f05050a, 0xb59a9a2f, 0x0907070e, 0x36121224, 0x9b80801b, 0x3de2e2df,
    0x26ebebcd, 0x6927274e, 0xcdb2b27f, 0x9f7575ea, 0x1b090912, 0x9e83831d,
    0x742c2c58, 0x2e1a1a34, 0x2d1b1b36, 0xb26e6edc, 0xee5a5ab4, 0xfba0a05b,
    0xf65252a4, 0x4d3b3b76, 0x61d6d6b7, 0xceb3b37d, 0x7b292952, 0x3ee3e3dd,
    0x712f2f5e, 0x97848413, 0xf55353a6, 0x68d1d1b9, 0x00000000, 0x2cededc1,
    0x60202040, 0x1ffcfce3, 0xc8b1b179, 0xed5b5bb6, 0xbe6a6ad4, 0x46cbcb8d,
    0xd9bebe67, 0x4b393972, 0xde4a4a94, 0xd44c4c98, 0xe85858b0, 0x4acfcf85,
    0x6bd0d0bb, 0x2aefefc5, 0xe5aaaa4f, 0x16fbfbed, 0xc5434386, 0xd74d4d9a,
    0x55333366, 0x94858511, 0xcf45458a, 0x10f9f9e9, 0x06020204, 0x817f7ffe,
    0xf05050a0, 0x443c3c78, 0xba9f9f25, 0xe3a8a84b, 0xf35151a2, 0xfea3a35d,
    0xc0404080, 0x8a8f8f05, 0xad92923f, 0xbc9d9d21, 0x48383870, 0x04f5f5f1,
    0xdfbcbc63, 0xc1b6b677, 0x75dadaaf, 0x63212142, 0x30101020, 0x1affffe5,
    0x0ef3f3fd, 0x6dd2d2bf, 0x4ccdcd81, 0x140c0c18, 0x35131326, 0x2fececc3,
    0xe15f5fbe, 0xa2979735, 0xcc444488, 0x3917172e, 0x57c4c493, 0xf2a7a755,
    0x827e7efc, 0x473d3d7a, 0xac6464c8, 0xe75d5dba, 0x2b191932, 0x957373e6,
    0xa06060c0, 0x98818119, 0xd14f4f9e, 0x7fdcdca3, 0x66222244, 0x7e2a2a54,
    0xab90903b, 0x8388880b, 0xca46468c, 0x29eeeec7, 0xd3b8b86b, 0x3c141428,
    0x79dedea7, 0xe25e5ebc, 0x1d0b0b16, 0x76dbdbad, 0x3be0e0db, 0x56323264,
    0x4e3a3a74, 0x1e0a0a14, 0xdb494992, 0x0a06060c, 0x6c242448, 0xe45c5cb8,
    0x5dc2c29f, 0x6ed3d3bd, 0xefacac43, 0xa66262c4, 0xa8919139, 0xa4959531,
    0x37e4e4d3, 0x8b7979f2, 0x32e7e7d5, 0x43c8c88b, 0x5937376e, 0xb76d6dda,
    0x8c8d8d01, 0x64d5d5b1, 0xd24e4e9c, 0xe0a9a949, 0xb46c6cd8, 0xfa5656ac,
    0x07f4f4f3, 0x25eaeacf, 0xaf6565ca, 0x8e7a7af4, 0xe9aeae47, 0x18080810,
    0xd5baba6f, 0x887878f0, 0x6f25254a, 0x722e2e5c, 0x241c1c38, 0xf1a6a657,
    0xc7b4b473, 0x51c6c697, 0x23e8e8cb, 0x7cdddda1, 0x9c7474e8, 0x211f1f3e,
    0xdd4b4b96, 0xdcbdbd61, 0x868b8b0d, 0x858a8a0f, 0x907070e0, 0x423e3e7c,
    0xc4b5b571, 0xaa6666cc, 0xd8484890, 0x05030306, 0x01f6f6f7, 0x120e0e1c,
    0xa36161c2, 0x5f35356a, 0xf95757ae, 0xd0b9b969, 0x91868617, 0x58c1c199,
    0x271d1d3a, 0xb99e9e27, 0x38e1e1d9, 0x13f8f8eb, 0xb398982b, 0x33111122,
    0xbb6969d2, 0x70d9d9a9, 0x898e8e07, 0xa7949433, 0xb69b9b2d, 0x221e1e3c,
    0x92878715, 0x20e9e9c9, 0x49cece87, 0xff5555aa, 0x78282850, 0x7adfdfa5,
    0x8f8c8c03, 0xf8a1a159, 0x80898909, 0x170d0d1a, 0xdabfbf65, 0x31e6e6d7,
    0xc6424284, 0xb86868d0, 0xc3414182, 0xb0999929, 0x772d2d5a, 0x110f0f1e,
    0xcbb0b07b, 0xfc5454a8, 0xd6bbbb6d, 0x3a16162c,
};

constexpr uint32_t te1[256] = {
    0x6363c6a5, 0x7c7cf884, 0x7777ee99, 0x7b7bf68d, 0xf2f2ff0d, 0x6b6bd6bd,
    0x6f6fdeb1, 0xc5c59154, 0x30306050, 0x01010203, 0x6767cea9, 0x2b2b567d,
    0xfefee719, 0xd7d7b562, 0xabab4de6, 0x7676ec9a, 0xcaca8f45, 0x82821f9d,
    0xc9c98940, 0x7d7dfa87, 0xfafaef15, 0x5959b2eb, 0x47478ec9, 0xf0f0fb0b,
    0xadad41ec, 0xd4d4b367, 0xa2a25ffd, 0xafaf45ea, 0x9c9c23bf, 0xa4a453f7,
    0x7272e496, 0xc0c09b5b, 0xb7b775c2, 0xfdfde11c, 0x93933dae, 0x26264c6a,
    0x36366c5a, 0x3f3f7e41, 0xf7f7f502, 0xcccc834f, 0x3434685c, 0xa5a551f4,
    0xe5e5d134, 0xf1f1f908, 0x7171e293, 0xd8d8ab73, 0x31316253, 0x15152a3f,
    0x0404080c, 0xc7c79552, 0x23234665, 0xc3c39d5e, 0x18183028, 0x969637a1,
    0x05050a0f, 0x9a9a2fb5, 0x07070e09, 0x12122436, 0x80801b9b, 0xe2e2df3d,
    0xebebcd26, 0x27274e69, 0xb2b27fcd, 0x7575ea9f, 0x0909121b, 0x83831d9e,
    0x2c2c5874, 0x1a1a342e, 0x1b1b362d, 0x6e6edcb2, 0x5a5ab4ee, 0xa0a05bfb,
    0x5252a4f6, 0x3b3b764d, 0xd6d6b761, 0xb3b37dce, 0x2929527b, 0xe3e3dd3e,
    0x2f2f5e71, 0x84841397, 0x5353a6f5, 0xd1d1b968, 0x00000000, 0xededc12c,
    0x20204060, 0xfcfce31f, 0xb1b179c8, 0x5b5bb6ed, 0x6a6ad4be, 0xcbcb8d46,
    0xbebe67d9, 0x3939724b, 0x4a4a94de, 0x4c4c98d4, 0x5858b0e8, 0xcfcf854a,
    0xd0d0bb6b, 0xefefc52a, 0xaaaa4fe5, 0xfbfbed16, 0x434386c5, 0x4d4d9ad7,
    0x33336655, 0x85851194, 0x45458acf, 0xf9f9e910, 0x02020406, 0x7f7ffe81,
    0x5050a0f0, 0x3c3c7844, 0x9f9f25ba, 0xa8a84be3, 0x5151a2f3, 0xa3a35dfe,
    0x404080c0, 0x8f8f058a, 0x92923fad, 0x9d9d21bc, 0x38387048, 0xf5f5f104,
    0xbcbc63df, 0xb6b677c1, 0xdadaaf75, 0x21214263, 0x10102030, 0xffffe51a,
    0xf3f3fd0e, 0xd2d2bf6d, 0xcdcd814c, 0x0c0c1814, 0x13132635, 0xececc32f,
    0x5f5fbee1, 0x979735a2, 0x444488cc, 0x17172e39, 0xc4c49357, 0xa7a755f2,
    0x7e7efc82, 0x3d3d7a47, 0x6464c8ac, 0x5d5dbae7, 0x1919322b, 0x7373e695,
    0x6060c0a0, 0x81811998, 0x4f4f9ed1, 0xdcdca37f, 0x22224466, 0x2a2a547e,
    0x90903bab, 0x88880b83, 0x46468cca, 0xeeeec729, 0xb8b86bd3, 0x1414283c,
    0xdedea779, 0x5e5ebce2, 0x0b0b161d, 0xdbdbad76, 0xe0e0db3b, 0x32326456,
    0x3a3a744e, 0x0a0a141e, 0x494992db, 0x06060c0a, 0x2424486c, 0x5c5cb8e4,
    0xc2c29f5d, 0xd3d3bd6e, 0xacac43ef, 0x6262c4a6, 0x919139a8, 0x959531a4,
    0xe4e4d337, 0x7979f28b, 0xe7e7d532, 0xc8c88b43, 0x37376e59, 0x6d6ddab7,
    0x8d8d018c, 0xd5d5b164, 0x4e4e9cd2, 0xa9a949e0, 0x6c6cd8b4, 0x5656acfa,
    0xf4f4f307, 0xeaeacf25, 0x6565caaf, 0x7a7af48e, 0xaeae47e9, 0x08081018,
    0xbaba6fd5, 0x7878f088, 0x25254a6f, 0x2e2e5c72, 0x1c1c3824, 0xa6a657f1,
    0xb4b473c7, 0xc6c69751, 0xe8e8cb23, 0xdddda17c, 0x7474e89c, 0x1f1f3e21,
    0x4b4b96dd, 0xbdbd61dc, 0x8b8b0d86, 0x8a8a0f85, 0x7070e090, 0x3e3e7c42,
    0xb5b571c4, 0x6666ccaa, 0x484890d8, 0x03030605, 0xf6f6f701, 0x0e0e1c12,
    0x6161c2a3, 0x35356a5f, 0x5757aef9, 0xb9b969d0, 0x86861791, 0xc1c19958,
    0x1d1d3a27, 0x9e9e27b9, 0xe1e1d938, 0xf8f8eb13, 0x98982bb3, 0x11112233,
    0x6969d2bb, 0xd9d9a970, 0x8e8e0789, 0x949433a7, 0x9b9b2db6, 0x1e1e3c22,
    0x87871592, 0xe9e9c920, 0xcece8749, 0x5555aaff, 0x28285078, 0xdfdfa57a,
    0x8c8c038f, 0xa1a159f8, 0x89890980, 0x0d0d1a17, 0xbfbf65da, 0xe6e6d731,
    0x424284c6, 0x6868d0b8, 0x414182c3, 0x999929b0, 0x2d2d5a77, 0x0f0f1e11,
    0xb0b07bcb, 0x5454a8fc, 0xbbbb6dd6, 0x16162c3a,
};

constexpr uint32_t te2[256] = {
    0x63c6a563, 0x7cf8847c, 0x77ee9977, 0x7bf68d7b, 0xf2ff0df2, 0x6bd6bd6b,
    0x6fdeb16f, 0xc59154c5, 0x30605030, 0x01020301, 0x67cea967, 0x2b567d2b,
    0xfee719fe, 0xd7b562d7, 0xab4de6ab, 0x76ec9a76, 0xca8f45ca, 0x821f9d82,
    0xc98940c9, 0x7dfa877d, 0xfaef15fa, 0x59b2eb59, 0x478ec947, 0xf0fb0bf0,
    0xad41ecad, 0xd4b367d4, 0xa25ffda2, 0xaf45eaaf, 0x9c23bf9c, 0xa453f7a4,
    0x72e49672, 0xc09b5bc0, 0xb775c2b7, 0xfde11cfd, 0x933dae93, 0x264c6a26,
    0x366c5a36, 0x3f7e413f, 0xf7f502f7, 0xcc834fcc, 0x34685c34, 0xa551f4a5,
    0xe5d134e5, 0xf1f908f1, 0x71e29371, 0xd8ab73d8, 0x31625331, 0x152a3f15,
    0x04080c04, 0xc79552c7, 0x23466523, 0xc39d5ec3, 0x18302818, 0x9637a196,
    0x050a0f05, 0x9a2fb59a, 0x070e0907, 0x12243612, 0x801b9b80, 0xe2df3de2,
    0xebcd26eb, 0x274e6927, 0xb27fcdb2, 0x75ea9f75, 0x09121b09, 0x831d9e83,
    0x2c58742c, 0x1a342e1a, 0x1b362d1b, 0x6edcb26e, 0x5ab4ee5a, 0xa05bfba0,
    0x52a4f652, 0x3b764d3b, 0xd6b761d6, 0xb37dceb3, 0x29527b29, 0xe3dd3ee3,
    0x2f5e712f, 0x84139784, 0x53a6f553, 0xd1b968d1, 0x00000000, 0xedc12ced,
    0x20406020, 0xfce31ffc, 0xb179c8b1, 0x5bb6ed5b, 0x6ad4be6a, 0xcb8d46cb,
    0xbe67d9be, 0x39724b39, 0x4a94de4a, 0x4c98d44c, 0x58b0e858, 0xcf854acf,
    0xd0bb6bd0, 0xefc52aef, 0xaa4fe5aa, 0xfbed16fb, 0x4386c543, 0x4d9ad74d,
    0x33665533, 0x85119485, 0x458acf45, 0xf9e910f9, 0x02040602, 0x7ffe817f,
    0x50a0f050, 0x3c78443c, 0x9f25ba9f, 0xa84be3a8, 0x51a2f351, 0xa35dfea3,
    0x4080c040, 0x8f058a8f, 0x923fad92, 0x9d21bc9d, 0x38704838, 0xf5f104f5,
    0xbc63dfbc, 0xb677c1b6, 0xdaaf75da, 0x21426321, 0x10203010, 0xffe51aff,
    0xf3fd0ef3, 0xd2bf6dd2, 0xcd814ccd, 0x0c18140c, 0x13263513, 0xecc32fec,
    0x5fbee15f, 0x9735a297, 0x4488cc44, 0x172e3917, 0xc49357c4, 0xa755f2a7,
    0x7efc827e, 0x3d7a473d, 0x64c8ac64, 0x5dbae75d, 0x19322b19, 0x73e69573,
    0x60c0a060, 0x81199881, 0x4f9ed14f, 0xdca37fdc, 0x22446622, 0x2a547e2a,
    0x903bab90, 0x880b8388, 0x468cca46, 0xeec729ee, 0xb86bd3b8, 0x14283c14,
    0xdea779de, 0x5ebce25e, 0x0b161d0b, 0xdbad76db, 0xe0db3be0, 0x32645632,
    0x3a744e3a, 0x0a141e0a, 0x4992db49, 0x060c0a06, 0x24486c24, 0x5cb8e45c,
    0xc29f5dc2, 0xd3bd6ed3, 0xac43efac, 0x62c4a662, 0x9139a891, 0x9531a495,
    0xe4d337e4, 0x79f28b79, 0xe7d532e7, 0xc88b43c8, 0x376e5937, 0x6ddab76d,
    0x8d018c8d, 0xd5b164d5, 0x4e9cd24e, 0xa949e0a9, 0x6cd8b46c, 0x56acfa56,
    0xf4f307f4, 0xeacf25ea, 0x65caaf65, 0x7af48e7a, 0xae47e9ae, 0x08101808,
    0xba6fd5ba, 0x78f08878, 0x254a6f25, 0x2e5c722e, 0x1c38241c, 0xa657f1a6,
    0xb473c7b4, 0xc69751c6, 0xe8cb23e8, 0xdda17cdd, 0x74e89c74, 0x1f3e211f,
    0x4b96dd4b, 0xbd61dcbd, 0x8b0d868b, 0x8a0f858a, 0x70e09070, 0x3e7c423e,
    0xb571c4b5, 0x66ccaa66, 0x4890d848, 0x03060503, 0xf6f701f6, 0x0e1c120e,
    0x61c2a361, 0x356a5f35, 0x57aef957, 0xb969d0b9, 0x86179186, 0xc19958c1,
    0x1d3a271d, 0x9e27b99e, 0xe1d938e1, 0xf8eb13f8, 0x982bb398, 0x11223311,
    0x69d2bb69, 0xd9a970d9, 0x8e07898e, 0x9433a794, 0x9b2db69b, 0x1e3c221e,
    0x87159287, 0xe9c920e9, 0xce8749ce, 0x55aaff55, 0x28507828, 0xdfa57adf,
    0x8c038f8c, 0xa159f8a1, 0x89098089, 0x0d1a170d, 0xbf65dabf, 0xe6d731e6,
    0x4284c642, 0x68d0b868, 0x4182c341, 0x9929b099, 0x2d5a772d, 0x0f1e110f,
    0xb07bcbb0, 0x54a8fc54, 0xbb6dd6bb, 0x162c3a16,
};

constexpr uint32_t te3[256] = {
    0xc6a56363, 0xf8847c7c, 0xee997777, 0xf68d7b7b, 0xff0df2f2, 0xd6bd6b6b,
    0xdeb16f6f, 0x9154c5c5, 0x60503030, 0x02030101, 0xcea96767, 0x567d2b2b,
    0xe719fefe, 0xb562d7d7, 0x4de6abab, 0xec9a7676, 0x8f45caca, 0x1f9d8282,
    0x8940c9c9, 0xfa877d7d, 0xef15fafa, 0xb2eb5959, 0x8ec94747, 0xfb0bf0f0,
    0x41ecadad, 0xb367d4d4, 0x5ffda2a2, 0x45eaafaf, 0x23bf9c9c, 0x53f7a4a4,
    0xe4967272, 0x9b5bc0c0, 0x75c2b7b7, 0xe11cfdfd, 0x3dae9393, 0x4c6a2626,
    0x6c5a3636, 0x7e413f3f, 0xf502f7f7, 0x834fcccc, 0x685c3434, 0x51f4a5a5,
    0xd134e5e5, 0xf908f1f1, 0xe2937171, 0xab73d8d8, 0x62533131, 0x2a3f1515,
    0x080c0404, 0x9552c7c7, 0x46652323, 0x9d5ec3c3, 0x30281818, 0x37a19696,
    0x0a0f0505, 0x2fb59a9a, 0x0e090707, 0x24361212, 0x1b9b8080, 0xdf3de2e2,
    0xcd26ebeb, 0x4e692727, 0x7fcdb2b2, 0xea9f7575, 0x121b0909, 0x1d9e8383,
    0x58742c2c, 0x342e1a1a, 0x362d1b1b, 0xdcb26e6e, 0xb4ee5a5a, 0x5bfba0a0,
    0xa4f65252, 0x764d3b3b, 0xb761d6d6, 0x7dceb3b3, 0x527b2929, 0xdd3ee3e3,
    0x5e712f2f, 0x13978484, 0xa6f55353, 0xb968d1d1, 0x00000000, 0xc12ceded,
    0x40602020, 0xe31ffcfc, 0x79c8b1b1, 0xb6ed5b5b, 0xd4be6a6a, 0x8d46cbcb,
    0x67d9bebe, 0x724b3939, 0x94de4a4a, 0x98d44c4c, 0xb0e85858, 0x854acfcf,
    0xbb6bd0d0, 0xc52aefef, 0x4fe5aaaa, 0xed16fbfb, 0x86c54343, 0x9ad74d4d,
    0x66553333, 0x11948585, 0x8acf4545, 0xe910f9f9, 0x04060202, 0xfe817f7f,
    0xa0f05050, 0x78443c3c, 0x25ba9f9f, 0x4be3a8a8, 0xa2f35151, 0x5dfea3a3,
    0x80c04040, 0x058a8f8f, 0x3fad9292, 0x21bc9d9d, 0x70483838, 0xf104f5f5,
    0x63dfbcbc, 0x77c1b6b6, 0xaf75dada, 0x42632121, 0x20301010, 0xe51affff,
    0xfd0ef3f3, 0xbf6dd2d2, 0x814ccdcd, 0x18140c0c, 0x26351313, 0xc32fecec,
    0xbee15f5f, 0x35a29797, 0x88cc4444, 0x2e391717, 0x9357c4c4, 0x55f2a7a7,
    0xfc827e7e, 0x7a473d3d, 0xc8ac6464, 0xbae75d5d, 0x322b1919, 0xe6957373,
    0xc0a06060, 0x19988181, 0x9ed14f4f, 0xa37fdcdc, 0x44662222, 0x547e2a2a,
    0x3bab9090, 0x0b838888, 0x8cca4646, 0xc729eeee, 0x6bd3b8b8, 0x283c1414,
    0xa779dede, 0xbce25e5e, 0x161d0b0b, 0xad76dbdb, 0xdb3be0e0, 0x64563232,
    0x744e3a3a, 0x141e0a0a, 0x92db4949, 0x0c0a0606, 0x486c2424, 0xb8e45c5c,
    0x9f5dc2c2, 0xbd6ed3d3, 0x43efacac, 0xc4a66262, 0x39a89191, 0x31a49595,
    0xd337e4e4, 0xf28b7979, 0xd532e7e7, 0x8b43c8c8, 0x6e593737, 0xdab76d6d,
    0x018c8d8d, 0xb164d5d5, 0x9cd24e4e, 0x49e0a9a9, 0xd8b46c6c, 0xacfa5656,
    0xf307f4f4, 0xcf25eaea, 0xcaaf6565, 0xf48e7a7a, 0x47e9aeae, 0x10180808,
    0x6fd5baba, 0xf0887878, 0x4a6f2525, 0x5c722e2e, 0x38241c1c, 0x57f1a6a6,
    0x73c7b4b4, 0x9751c6c6, 0xcb23e8e8, 0xa17cdddd, 0xe89c7474, 0x3e211f1f,
    0x96dd4b4b, 0x61dcbdbd, 0x0d868b8b, 0x0f858a8a, 0xe0907070, 0x7c423e3e,
    0x71c4b5b5, 0xccaa6666, 0x90d84848, 0x06050303, 0xf701f6f6, 0x1c120e0e,
    0xc2a36161, 0x6a5f3535, 0xaef95757, 0x69d0b9b9, 0x17918686, 0x9958c1c1,
    0x3a271d1d, 0x27b99e9e, 0xd938e1e1, 0xeb13f8f8, 0x2bb39898, 0x22331111,
    0xd2bb6969, 0xa970d9d9, 0x07898e8e, 0x33a79494, 0x2db69b9b, 0x3c221e1e,
    0x15928787, 0xc920e9e9, 0x8749cece, 0xaaff5555, 0x50782828, 0xa57adfdf,
    0x038f8c8c, 0x59f8a1a1, 0x09808989, 0x1a170d0d, 0x65dabfbf, 0xd731e6e6,
    0x84c64242, 0xd0b86868, 0x82c34141, 0x29b09999, 0x5a772d2d, 0x1e110f0f,
    0x7bcbb0b0, 0xa8fc5454, 0x6dd6bbbb, 0x2c3a1616,
};

// Software implementation of the Vector128 class, using uint32_t
// as an underlying vector register.
struct alignas(16) Vector128 {
  uint32_t s[4];
};

inline ABSL_RANDOM_INTERNAL_ATTRIBUTE_ALWAYS_INLINE Vector128
Vector128Load(const void* from) {
  Vector128 result;
  std::memcpy(result.s, from, sizeof(Vector128));
  return result;
}

inline ABSL_RANDOM_INTERNAL_ATTRIBUTE_ALWAYS_INLINE void Vector128Store(
    const Vector128& v, void* to) {
  std::memcpy(to, v.s, sizeof(Vector128));
}

// One round of AES. "round_key" is a public constant for breaking the
// symmetry of AES (ensures previously equal columns differ afterwards).
inline ABSL_RANDOM_INTERNAL_ATTRIBUTE_ALWAYS_INLINE Vector128
AesRound(const Vector128& state, const Vector128& round_key) {
  Vector128 result;
#ifdef ABSL_IS_LITTLE_ENDIAN
  result.s[0] = round_key.s[0] ^                  //
                te0[uint8_t(state.s[0])] ^        //
                te1[uint8_t(state.s[1] >> 8)] ^   //
                te2[uint8_t(state.s[2] >> 16)] ^  //
                te3[uint8_t(state.s[3] >> 24)];
  result.s[1] = round_key.s[1] ^                  //
                te0[uint8_t(state.s[1])] ^        //
                te1[uint8_t(state.s[2] >> 8)] ^   //
                te2[uint8_t(state.s[3] >> 16)] ^  //
                te3[uint8_t(state.s[0] >> 24)];
  result.s[2] = round_key.s[2] ^                  //
                te0[uint8_t(state.s[2])] ^        //
                te1[uint8_t(state.s[3] >> 8)] ^   //
                te2[uint8_t(state.s[0] >> 16)] ^  //
                te3[uint8_t(state.s[1] >> 24)];
  result.s[3] = round_key.s[3] ^                  //
                te0[uint8_t(state.s[3])] ^        //
                te1[uint8_t(state.s[0] >> 8)] ^   //
                te2[uint8_t(state.s[1] >> 16)] ^  //
                te3[uint8_t(state.s[2] >> 24)];
#else
  result.s[0] = round_key.s[0] ^                  //
                te0[uint8_t(state.s[0])] ^        //
                te1[uint8_t(state.s[3] >> 8)] ^   //
                te2[uint8_t(state.s[2] >> 16)] ^  //
                te3[uint8_t(state.s[1] >> 24)];
  result.s[1] = round_key.s[1] ^                  //
                te0[uint8_t(state.s[1])] ^        //
                te1[uint8_t(state.s[0] >> 8)] ^   //
                te2[uint8_t(state.s[3] >> 16)] ^  //
                te3[uint8_t(state.s[2] >> 24)];
  result.s[2] = round_key.s[2] ^                  //
                te0[uint8_t(state.s[2])] ^        //
                te1[uint8_t(state.s[1] >> 8)] ^   //
                te2[uint8_t(state.s[0] >> 16)] ^  //
                te3[uint8_t(state.s[3] >> 24)];
  result.s[3] = round_key.s[3] ^                  //
                te0[uint8_t(state.s[3])] ^        //
                te1[uint8_t(state.s[2] >> 8)] ^   //
                te2[uint8_t(state.s[1] >> 16)] ^  //
                te3[uint8_t(state.s[0] >> 24)];
#endif
  return result;
}

using ::absl::random_internal::RandenTraits;

// The improved Feistel block shuffle function for 16 blocks.
inline ABSL_RANDOM_INTERNAL_ATTRIBUTE_ALWAYS_INLINE void BlockShuffle(
    absl::uint128* state) {
  static_assert(RandenTraits::kFeistelBlocks == 16,
                "Feistel block shuffle only works for 16 blocks.");

  constexpr size_t shuffle[RandenTraits::kFeistelBlocks] = {
      7, 2, 13, 4, 11, 8, 3, 6, 15, 0, 9, 10, 1, 14, 5, 12};

  // The fully unrolled loop without the memcpy improves the speed by about
  // 30% over the equivalent:
#if 0
  absl::uint128 source[RandenTraits::kFeistelBlocks];
  std::memcpy(source, state, sizeof(source));
  for (size_t i = 0; i < RandenTraits::kFeistelBlocks; i++) {
    const absl::uint128 v0 = source[shuffle[i]];
    state[i] = v0;
  }
  return;
#endif

  const absl::uint128 v0 = state[shuffle[0]];
  const absl::uint128 v1 = state[shuffle[1]];
  const absl::uint128 v2 = state[shuffle[2]];
  const absl::uint128 v3 = state[shuffle[3]];
  const absl::uint128 v4 = state[shuffle[4]];
  const absl::uint128 v5 = state[shuffle[5]];
  const absl::uint128 v6 = state[shuffle[6]];
  const absl::uint128 v7 = state[shuffle[7]];
  const absl::uint128 w0 = state[shuffle[8]];
  const absl::uint128 w1 = state[shuffle[9]];
  const absl::uint128 w2 = state[shuffle[10]];
  const absl::uint128 w3 = state[shuffle[11]];
  const absl::uint128 w4 = state[shuffle[12]];
  const absl::uint128 w5 = state[shuffle[13]];
  const absl::uint128 w6 = state[shuffle[14]];
  const absl::uint128 w7 = state[shuffle[15]];
  state[0] = v0;
  state[1] = v1;
  state[2] = v2;
  state[3] = v3;
  state[4] = v4;
  state[5] = v5;
  state[6] = v6;
  state[7] = v7;
  state[8] = w0;
  state[9] = w1;
  state[10] = w2;
  state[11] = w3;
  state[12] = w4;
  state[13] = w5;
  state[14] = w6;
  state[15] = w7;
}

// Feistel round function using two AES subrounds. Very similar to F()
// from Simpira v2, but with independent subround keys. Uses 17 AES rounds
// per 16 bytes (vs. 10 for AES-CTR). Computing eight round functions in
// parallel hides the 7-cycle AESNI latency on HSW. Note that the Feistel
// XORs are 'free' (included in the second AES instruction).
inline ABSL_RANDOM_INTERNAL_ATTRIBUTE_ALWAYS_INLINE const absl::uint128*
FeistelRound(absl::uint128* ABSL_RANDOM_INTERNAL_RESTRICT state,
             const absl::uint128* ABSL_RANDOM_INTERNAL_RESTRICT keys) {
  for (size_t branch = 0; branch < RandenTraits::kFeistelBlocks; branch += 4) {
    const Vector128 s0 = Vector128Load(state + branch);
    const Vector128 s1 = Vector128Load(state + branch + 1);
    const Vector128 f0 = AesRound(s0, Vector128Load(keys));
    keys++;
    const Vector128 o1 = AesRound(f0, s1);
    Vector128Store(o1, state + branch + 1);

    // Manually unroll this loop once. about 10% better than not unrolled.
    const Vector128 s2 = Vector128Load(state + branch + 2);
    const Vector128 s3 = Vector128Load(state + branch + 3);
    const Vector128 f2 = AesRound(s2, Vector128Load(keys));
    keys++;
    const Vector128 o3 = AesRound(f2, s3);
    Vector128Store(o3, state + branch + 3);
  }
  return keys;
}

// Cryptographic permutation based via type-2 Generalized Feistel Network.
// Indistinguishable from ideal by chosen-ciphertext adversaries using less than
// 2^64 queries if the round function is a PRF. This is similar to the b=8 case
// of Simpira v2, but more efficient than its generic construction for b=16.
inline ABSL_RANDOM_INTERNAL_ATTRIBUTE_ALWAYS_INLINE void Permute(
    absl::uint128* state,
    const absl::uint128* ABSL_RANDOM_INTERNAL_RESTRICT keys) {
  for (size_t round = 0; round < RandenTraits::kFeistelRounds; ++round) {
    keys = FeistelRound(state, keys);
    BlockShuffle(state);
  }
}

}  // namespace

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace random_internal {

const void* RandenSlow::GetKeys() {
  // Round keys for one AES per Feistel round and branch.
  // The canonical implementation uses first digits of Pi.
#ifdef ABSL_IS_LITTLE_ENDIAN
  return kRandenRoundKeys;
#else
  return kRandenRoundKeysBE;
#endif
}

void RandenSlow::Absorb(const void* seed_void, void* state_void) {
  auto* state =
      reinterpret_cast<uint64_t * ABSL_RANDOM_INTERNAL_RESTRICT>(state_void);
  const auto* seed =
      reinterpret_cast<const uint64_t * ABSL_RANDOM_INTERNAL_RESTRICT>(
          seed_void);

  constexpr size_t kCapacityBlocks =
      RandenTraits::kCapacityBytes / sizeof(uint64_t);
  static_assert(
      kCapacityBlocks * sizeof(uint64_t) == RandenTraits::kCapacityBytes,
      "Not i*V");

  for (size_t i = kCapacityBlocks;
       i < RandenTraits::kStateBytes / sizeof(uint64_t); ++i) {
    state[i] ^= seed[i - kCapacityBlocks];
  }
}

void RandenSlow::Generate(const void* keys_void, void* state_void) {
  static_assert(RandenTraits::kCapacityBytes == sizeof(absl::uint128),
                "Capacity mismatch");

  auto* state = reinterpret_cast<absl::uint128*>(state_void);
  const auto* keys = reinterpret_cast<const absl::uint128*>(keys_void);

  const absl::uint128 prev_inner = state[0];

  Permute(state, keys);

  // Ensure backtracking resistance.
  *state ^= prev_inner;
}

}  // namespace random_internal
ABSL_NAMESPACE_END
}  // namespace absl