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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// SHA256 block step.
// In its own file so that a faster assembly or C version
// can be substituted easily.

package sha256

var _K = []uint32{
        0x428a2f98,
        0x71374491,
        0xb5c0fbcf,
        0xe9b5dba5,
        0x3956c25b,
        0x59f111f1,
        0x923f82a4,
        0xab1c5ed5,
        0xd807aa98,
        0x12835b01,
        0x243185be,
        0x550c7dc3,
        0x72be5d74,
        0x80deb1fe,
        0x9bdc06a7,
        0xc19bf174,
        0xe49b69c1,
        0xefbe4786,
        0x0fc19dc6,
        0x240ca1cc,
        0x2de92c6f,
        0x4a7484aa,
        0x5cb0a9dc,
        0x76f988da,
        0x983e5152,
        0xa831c66d,
        0xb00327c8,
        0xbf597fc7,
        0xc6e00bf3,
        0xd5a79147,
        0x06ca6351,
        0x14292967,
        0x27b70a85,
        0x2e1b2138,
        0x4d2c6dfc,
        0x53380d13,
        0x650a7354,
        0x766a0abb,
        0x81c2c92e,
        0x92722c85,
        0xa2bfe8a1,
        0xa81a664b,
        0xc24b8b70,
        0xc76c51a3,
        0xd192e819,
        0xd6990624,
        0xf40e3585,
        0x106aa070,
        0x19a4c116,
        0x1e376c08,
        0x2748774c,
        0x34b0bcb5,
        0x391c0cb3,
        0x4ed8aa4a,
        0x5b9cca4f,
        0x682e6ff3,
        0x748f82ee,
        0x78a5636f,
        0x84c87814,
        0x8cc70208,
        0x90befffa,
        0xa4506ceb,
        0xbef9a3f7,
        0xc67178f2,
}

func _Block(dig *digest, p []byte) int {
        var w [64]uint32
        n := 0
        h0, h1, h2, h3, h4, h5, h6, h7 := dig.h[0], dig.h[1], dig.h[2], dig.h[3], dig.h[4], dig.h[5], dig.h[6], dig.h[7]
        for len(p) >= _Chunk {
                // Can interlace the computation of w with the
                // rounds below if needed for speed.
                for i := 0; i < 16; i++ {
                        j := i * 4
                        w[i] = uint32(p[j])<<24 | uint32(p[j+1])<<16 | uint32(p[j+2])<<8 | uint32(p[j+3])
                }
                for i := 16; i < 64; i++ {
                        t1 := (w[i-2]>>17 | w[i-2]<<(32-17)) ^ (w[i-2]>>19 | w[i-2]<<(32-19)) ^ (w[i-2] >> 10)

                        t2 := (w[i-15]>>7 | w[i-15]<<(32-7)) ^ (w[i-15]>>18 | w[i-15]<<(32-18)) ^ (w[i-15] >> 3)

                        w[i] = t1 + w[i-7] + t2 + w[i-16]
                }

                a, b, c, d, e, f, g, h := h0, h1, h2, h3, h4, h5, h6, h7

                for i := 0; i < 64; i++ {
                        t1 := h + ((e>>6 | e<<(32-6)) ^ (e>>11 | e<<(32-11)) ^ (e>>25 | e<<(32-25))) + ((e & f) ^ (^e & g)) + _K[i] + w[i]

                        t2 := ((a>>2 | a<<(32-2)) ^ (a>>13 | a<<(32-13)) ^ (a>>22 | a<<(32-22))) + ((a & b) ^ (a & c) ^ (b & c))

                        h = g
                        g = f
                        f = e
                        e = d + t1
                        d = c
                        c = b
                        b = a
                        a = t1 + t2
                }

                h0 += a
                h1 += b
                h2 += c
                h3 += d
                h4 += e
                h5 += f
                h6 += g
                h7 += h

                p = p[_Chunk:]
                n += _Chunk
        }

        dig.h[0], dig.h[1], dig.h[2], dig.h[3], dig.h[4], dig.h[5], dig.h[6], dig.h[7] = h0, h1, h2, h3, h4, h5, h6, h7
        return n
}