// Copyright (c) 2019-2023 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
// SHA256 block step.
// This is the generic version with no architecture optimizations.
// In its own file so that an architecture
// optimized version can be substituted
module sha256

import math.bits

const (
	_k = [
		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,
	]
)

fn block_generic(mut dig Digest, p_ []u8) {
	unsafe {
		mut p := p_
		mut w := []u32{len: (64)}
		mut h0 := dig.h[0]
		mut h1 := dig.h[1]
		mut h2 := dig.h[2]
		mut h3 := dig.h[3]
		mut h4 := dig.h[4]
		mut h5 := dig.h[5]
		mut h6 := dig.h[6]
		mut h7 := dig.h[7]
		for p.len >= chunk {
			// Can interlace the computation of w with the
			// rounds below if needed for speed.
			for i in 0 .. 16 {
				j := i * 4
				w[i] = u32(p[j]) << 24 | u32(p[j + 1]) << 16 | u32(p[j + 2]) << 8 | u32(p[j + 3])
			}
			for i := 16; i < 64; i++ {
				v1 := w[i - 2]
				t1 := (bits.rotate_left_32(v1, -17)) ^ (bits.rotate_left_32(v1, -19)) ^ (v1 >> 10)
				v2 := w[i - 15]
				t2 := (bits.rotate_left_32(v2, -7)) ^ (bits.rotate_left_32(v2, -18)) ^ (v2 >> 3)
				w[i] = t1 + w[i - 7] + t2 + w[i - 16]
			}
			mut a := h0
			mut b := h1
			mut c := h2
			mut d := h3
			mut e := h4
			mut f := h5
			mut g := h6
			mut h := h7
			for i in 0 .. 64 {
				t1 := h +
					((bits.rotate_left_32(e, -6)) ^ (bits.rotate_left_32(e, -11)) ^ (bits.rotate_left_32(e, -25))) +
					((e & f) ^ (~e & g)) + u32(sha256._k[i]) + w[i]
				t2 :=
					((bits.rotate_left_32(a, -2)) ^ (bits.rotate_left_32(a, -13)) ^ (bits.rotate_left_32(a, -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
			if chunk >= p.len {
				p = []
			} else {
				p = p[chunk..]
			}
		}
		dig.h[0] = h0
		dig.h[1] = h1
		dig.h[2] = h2
		dig.h[3] = h3
		dig.h[4] = h4
		dig.h[5] = h5
		dig.h[6] = h6
		dig.h[7] = h7
	}
}
