/*
 * SHA1 routine optimized to do word accesses rather than byte accesses,
 * and to avoid unnecessary copies into the context array.
 *
 * This was based on the git SHA1 implementation.
 */

#include <linux/kernel.h>
#include <linux/bitops.h>

/*
 * If you have 32 registers or more, the compiler can (and should)
 * try to change the array[] accesses into registers. However, on
 * machines with less than ~25 registers, that won't really work,
 * and at least gcc will make an unholy mess of it.
 *
 * So to avoid that mess which just slows things down, we force
 * the stores to memory to actually happen (we might be better off
 * with a 'W(t)=(val);asm("":"+m" (W(t))' there instead, as
 * suggested by Artur Skawina - that will also make gcc unable to
 * try to do the silly "optimize away loads" part because it won't
 * see what the value will be).
 *
 * Ben Herrenschmidt reports that on PPC, the C version comes close
 * to the optimized asm with this (ie on PPC you don't want that
 * 'volatile', since there are lots of registers).
 *
 * On ARM we get the best code generation by forcing a full memory barrier
 * between each SHA_ROUND, otherwise gcc happily get wild with spilling and
 * the stack frame size simply explode and performance goes down the drain.
 */

#ifdef CONFIG_X86
#define setW(x, val) (*(volatile __u32*)&W(x) = (val))
#elif defined(CONFIG_ARM)
#define setW(x, val)          \
  do {                        \
    W(x) = (val);             \
    __asm__("" ::: "memory"); \
  } while (0)
#else
#define setW(x, val) (W(x) = (val))
#endif

/* This "rolls" over the 512-bit array */
#define W(x) (array[(x)&15])

static inline u32 __get_unaligned_be32(const u8* p) {
  return p[0] << 24 | p[1] << 16 | p[2] << 8 | p[3];
}

static inline u32 get_unaligned_be32(const void* p) {
  return __get_unaligned_be32((const u8*)p);
}

/*
 * Where do we get the source from? The first 16 iterations get it from
 * the input data, the next mix it from the 512-bit array.
 */
#define SHA_SRC(t) get_unaligned_be32((__u32*)data + t)
#define SHA_MIX(t) rol32(W(t + 13) ^ W(t + 8) ^ W(t + 2) ^ W(t), 1)

#define SHA_ROUND(t, input, fn, constant, A, B, C, D, E) \
  do {                                                   \
    __u32 TEMP = input(t);                               \
    setW(t, TEMP);                                       \
    E += TEMP + rol32(A, 5) + (fn) + (constant);         \
    B = ror32(B, 2);                                     \
  } while (0)

#define T_0_15(t, A, B, C, D, E) \
  SHA_ROUND(t, SHA_SRC, (((C ^ D) & B) ^ D), 0x5a827999, A, B, C, D, E)
#define T_16_19(t, A, B, C, D, E) \
  SHA_ROUND(t, SHA_MIX, (((C ^ D) & B) ^ D), 0x5a827999, A, B, C, D, E)
#define T_20_39(t, A, B, C, D, E) \
  SHA_ROUND(t, SHA_MIX, (B ^ C ^ D), 0x6ed9eba1, A, B, C, D, E)
#define T_40_59(t, A, B, C, D, E) \
  SHA_ROUND(t, SHA_MIX, ((B & C) + (D & (B ^ C))), 0x8f1bbcdc, A, B, C, D, E)
#define T_60_79(t, A, B, C, D, E) \
  SHA_ROUND(t, SHA_MIX, (B ^ C ^ D), 0xca62c1d6, A, B, C, D, E)

/**
 * sha_transform - single block SHA1 transform
 *
 * @digest: 160 bit digest to update
 * @data:   512 bits of data to hash
 * @array:  16 words of workspace (see note)
 *
 * This function generates a SHA1 digest for a single 512-bit block.
 * Be warned, it does not handle padding and message digest, do not
 * confuse it with the full FIPS 180-1 digest algorithm for variable
 * length messages.
 *
 * Note: If the hash is security sensitive, the caller should be sure
 * to clear the workspace. This is left to the caller to avoid
 * unnecessary clears between chained hashing operations.
 */
void sha_transform(__u32* digest, const char* data, __u32* array) {
  __u32 A, B, C, D, E;

  A = digest[0];
  B = digest[1];
  C = digest[2];
  D = digest[3];
  E = digest[4];

  /* Round 1 - iterations 0-16 take their input from 'data' */
  T_0_15(0, A, B, C, D, E);
  T_0_15(1, E, A, B, C, D);
  T_0_15(2, D, E, A, B, C);
  T_0_15(3, C, D, E, A, B);
  T_0_15(4, B, C, D, E, A);
  T_0_15(5, A, B, C, D, E);
  T_0_15(6, E, A, B, C, D);
  T_0_15(7, D, E, A, B, C);
  T_0_15(8, C, D, E, A, B);
  T_0_15(9, B, C, D, E, A);
  T_0_15(10, A, B, C, D, E);
  T_0_15(11, E, A, B, C, D);
  T_0_15(12, D, E, A, B, C);
  T_0_15(13, C, D, E, A, B);
  T_0_15(14, B, C, D, E, A);
  T_0_15(15, A, B, C, D, E);

  /* Round 1 - tail. Input from 512-bit mixing array */
  T_16_19(16, E, A, B, C, D);
  T_16_19(17, D, E, A, B, C);
  T_16_19(18, C, D, E, A, B);
  T_16_19(19, B, C, D, E, A);

  /* Round 2 */
  T_20_39(20, A, B, C, D, E);
  T_20_39(21, E, A, B, C, D);
  T_20_39(22, D, E, A, B, C);
  T_20_39(23, C, D, E, A, B);
  T_20_39(24, B, C, D, E, A);
  T_20_39(25, A, B, C, D, E);
  T_20_39(26, E, A, B, C, D);
  T_20_39(27, D, E, A, B, C);
  T_20_39(28, C, D, E, A, B);
  T_20_39(29, B, C, D, E, A);
  T_20_39(30, A, B, C, D, E);
  T_20_39(31, E, A, B, C, D);
  T_20_39(32, D, E, A, B, C);
  T_20_39(33, C, D, E, A, B);
  T_20_39(34, B, C, D, E, A);
  T_20_39(35, A, B, C, D, E);
  T_20_39(36, E, A, B, C, D);
  T_20_39(37, D, E, A, B, C);
  T_20_39(38, C, D, E, A, B);
  T_20_39(39, B, C, D, E, A);

  /* Round 3 */
  T_40_59(40, A, B, C, D, E);
  T_40_59(41, E, A, B, C, D);
  T_40_59(42, D, E, A, B, C);
  T_40_59(43, C, D, E, A, B);
  T_40_59(44, B, C, D, E, A);
  T_40_59(45, A, B, C, D, E);
  T_40_59(46, E, A, B, C, D);
  T_40_59(47, D, E, A, B, C);
  T_40_59(48, C, D, E, A, B);
  T_40_59(49, B, C, D, E, A);
  T_40_59(50, A, B, C, D, E);
  T_40_59(51, E, A, B, C, D);
  T_40_59(52, D, E, A, B, C);
  T_40_59(53, C, D, E, A, B);
  T_40_59(54, B, C, D, E, A);
  T_40_59(55, A, B, C, D, E);
  T_40_59(56, E, A, B, C, D);
  T_40_59(57, D, E, A, B, C);
  T_40_59(58, C, D, E, A, B);
  T_40_59(59, B, C, D, E, A);

  /* Round 4 */
  T_60_79(60, A, B, C, D, E);
  T_60_79(61, E, A, B, C, D);
  T_60_79(62, D, E, A, B, C);
  T_60_79(63, C, D, E, A, B);
  T_60_79(64, B, C, D, E, A);
  T_60_79(65, A, B, C, D, E);
  T_60_79(66, E, A, B, C, D);
  T_60_79(67, D, E, A, B, C);
  T_60_79(68, C, D, E, A, B);
  T_60_79(69, B, C, D, E, A);
  T_60_79(70, A, B, C, D, E);
  T_60_79(71, E, A, B, C, D);
  T_60_79(72, D, E, A, B, C);
  T_60_79(73, C, D, E, A, B);
  T_60_79(74, B, C, D, E, A);
  T_60_79(75, A, B, C, D, E);
  T_60_79(76, E, A, B, C, D);
  T_60_79(77, D, E, A, B, C);
  T_60_79(78, C, D, E, A, B);
  T_60_79(79, B, C, D, E, A);

  digest[0] += A;
  digest[1] += B;
  digest[2] += C;
  digest[3] += D;
  digest[4] += E;
}

/**
 * sha_init - initialize the vectors for a SHA1 digest
 * @buf: vector to initialize
 */
void sha_init(__u32* buf) {
  buf[0] = 0x67452301;
  buf[1] = 0xefcdab89;
  buf[2] = 0x98badcfe;
  buf[3] = 0x10325476;
  buf[4] = 0xc3d2e1f0;
}