// -*- go -*-
//
// Copyright (c) 2020-2023 Markku Rossi
//
// All rights reserved.
//

// Package sha512 implements the SHA-384, SHA-512, SHA-512/224, and
// SHA-512/256 cryptographic hash functions.
package sha512

const (
	// The size of a SHA512 checksum in bytes.
	Size = 64

	// BlockSize is the block size, in bytes, of the SHA-512/224,
	// SHA-512/256, SHA-384 and SHA-512 hash functions.
	BlockSize = 128

	init = 0x6a09e667f3bcc908bb67ae8584caa73b3c6ef372fe94f82ba54ff53a5f1d36f1510e527fade682d19b05688c2b3e6c1f1f83d9abfb41bd6b5be0cd19137e2179
)

// Sum512 returns the SHA512 checksum of the data.
func Sum512(data []byte) [Size]byte {
	var state uint512 = init
	var block uint1024
	var hash [Size]byte

	var pad [BlockSize]byte
	pad[0] = 0x80

	for i := 0; i < len(data); i++ {
		block <<= 8
		block = block | uint1024(data[i])

		if (i+1)%BlockSize == 0 {
			state = Block(block, state)
			block = 0
		}
	}
	if len(data)%BlockSize < 112 {
		for i := len(data) % BlockSize; i < 112; i++ {
			block <<= 8
			block |= uint1024(pad[i-len(data)%BlockSize])
		}
	} else {
		for i := len(data) % BlockSize; i < BlockSize; i++ {
			block <<= 8
			block |= uint1024(pad[i-len(data)%BlockSize])
		}
		state = Block(block, state)
		block = 0
	}
	// Length in bits.
	block <<= 128
	block |= uint1024(len(data) << 3)

	state = Block(block, state)

	for i := 0; i < Size; i++ {
		hash[Size-i-1] = byte(state & 0xff)
		state >>= 8
	}
	return hash
}

// Block adds a new SHA-512 block to the state.
func Block(block uint1024, state uint512) uint512 {
	return native("sha512.qclc", block, state)
}