golang.org/x/arch@v0.17.0/s390x/s390xasm/field.go (about)

     1  // Copyright 2024 The Go Authors.  All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package s390xasm
     6  
     7  import (
     8  	"fmt"
     9  )
    10  
    11  // A BitField is a bit-field in a 64-bit double word.
    12  // Bits are counted from 0 from the MSB to 63 as the LSB.
    13  type BitField struct {
    14  	Offs uint8 // the offset of the left-most bit.
    15  	Bits uint8 // length in bits.
    16  }
    17  
    18  func (b BitField) String() string {
    19  	if b.Bits > 1 {
    20  		return fmt.Sprintf("[%d:%d]", b.Offs, int(b.Offs+b.Bits)-1)
    21  	} else if b.Bits == 1 {
    22  		return fmt.Sprintf("[%d]", b.Offs)
    23  	} else {
    24  		return fmt.Sprintf("[%d, len=0]", b.Offs)
    25  	}
    26  }
    27  
    28  // Parse extracts the bitfield b from i, and return it as an unsigned integer.
    29  // Parse will panic if b is invalid.
    30  func (b BitField) Parse(i uint64) uint64 {
    31  	if b.Bits > 64 || b.Bits == 0 || b.Offs > 63 || b.Offs+b.Bits > 64 {
    32  		panic(fmt.Sprintf("invalid bitfiled %v", b))
    33  	}
    34  	if b.Bits == 20 {
    35  		return ((((i >> (64 - b.Offs - b.Bits)) & ((1 << 8) - 1)) << 12) | ((i >> (64 - b.Offs - b.Bits + 8)) & 0xFFF))
    36  
    37  	} else {
    38  		return (i >> (64 - b.Offs - b.Bits)) & ((1 << b.Bits) - 1)
    39  	}
    40  }
    41  
    42  // ParseSigned extracts the bitfield b from i, and return it as a signed integer.
    43  // ParseSigned will panic if b is invalid.
    44  func (b BitField) ParseSigned(i uint64) int64 {
    45  	u := int64(b.Parse(i))
    46  	return u << (64 - b.Bits) >> (64 - b.Bits)
    47  }