// Copyright 2014 The go-ethereum Authors
// (original work)
// Copyright 2024 The Erigon Authors
// (modifications)
// This file is part of Erigon.
//
// Erigon is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Erigon is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with Erigon. If not, see <http://www.gnu.org/licenses/>.

package vm

import (
	"github.com/holiman/uint256"

	"github.com/erigontech/erigon/common"
	"github.com/erigontech/erigon/common/math"
)

// calcMemSize64 calculates the required memory size, and returns
// the size and whether the result overflowed uint64
func calcMemSize64(off, l *uint256.Int) (uint64, bool) {
	if !l.IsUint64() {
		return 0, true
	}
	return calcMemSize64WithUint(off, l.Uint64())
}

// calcMemSize64WithUint calculates the required memory size, and returns
// the size and whether the result overflowed uint64
// Identical to calcMemSize64, but length is a uint64
func calcMemSize64WithUint(off *uint256.Int, length64 uint64) (uint64, bool) {
	// if length is zero, memsize is always zero, regardless of offset
	if length64 == 0 {
		return 0, false
	}
	// Check that offset doesn't overflow
	offset64, overflow := off.Uint64WithOverflow()
	if overflow {
		return 0, true
	}
	val := offset64 + length64
	// if value < either of it's parts, then it overflowed
	return val, val < offset64
}

// getData returns a slice from the data based on the start and size and pads
// up to size with zero's. This function is overflow safe.
func getData(data []byte, start uint64, size uint64) []byte {
	length := uint64(len(data))
	if start > length {
		start = length
	}
	end, overflow := math.SafeAdd(start, size)
	if end > length || overflow {
		end = length
	}
	return common.RightPadBytes(data[start:end], int(size))
}

// ToWordSize returns the ceiled word size required for memory expansion.
func ToWordSize(size uint64) uint64 {
	if size > math.MaxUint64-31 {
		return math.MaxUint64/32 + 1
	}

	return (size + 31) / 32
}
