// Copyright 2024 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.

package s390xasm

import (
	"fmt"
)

// A BitField is a bit-field in a 64-bit double word.
// Bits are counted from 0 from the MSB to 63 as the LSB.
type BitField struct {
	Offs uint8 // the offset of the left-most bit.
	Bits uint8 // length in bits.
}

func (b BitField) String() string {
	if b.Bits > 1 {
		return fmt.Sprintf("[%d:%d]", b.Offs, int(b.Offs+b.Bits)-1)
	} else if b.Bits == 1 {
		return fmt.Sprintf("[%d]", b.Offs)
	} else {
		return fmt.Sprintf("[%d, len=0]", b.Offs)
	}
}

// Parse extracts the bitfield b from i, and return it as an unsigned integer.
// Parse will panic if b is invalid.
func (b BitField) Parse(i uint64) uint64 {
	if b.Bits > 64 || b.Bits == 0 || b.Offs > 63 || b.Offs+b.Bits > 64 {
		panic(fmt.Sprintf("invalid bitfiled %v", b))
	}
	if b.Bits == 20 {
		return ((((i >> (64 - b.Offs - b.Bits)) & ((1 << 8) - 1)) << 12) | ((i >> (64 - b.Offs - b.Bits + 8)) & 0xFFF))

	} else {
		return (i >> (64 - b.Offs - b.Bits)) & ((1 << b.Bits) - 1)
	}
}

// ParseSigned extracts the bitfield b from i, and return it as a signed integer.
// ParseSigned will panic if b is invalid.
func (b BitField) ParseSigned(i uint64) int64 {
	u := int64(b.Parse(i))
	return u << (64 - b.Bits) >> (64 - b.Bits)
}