go field 源码
golang field 代码
文件路径：/src/cmd/vendor/golang.org/x/arch/ppc64/ppc64asm/field.go
// Copyright 2014 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 ppc64asm
import (
"fmt"
"strings"
)
// A BitField is a bit-field in a 32-bit word.
// Bits are counted from 0 from the MSB to 31 as the LSB.
type BitField struct {
Offs uint8 // the offset of the left-most bit.
Bits uint8 // length in bits.
// This instruction word holding this field.
// It is always 0 for ISA < 3.1 instructions. It is
// in decoding order. (0 == prefix, 1 == suffix on ISA 3.1)
Word uint8
}
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 [2]uint32) uint32 {
if b.Bits > 32 || b.Bits == 0 || b.Offs > 31 || b.Offs+b.Bits > 32 {
panic(fmt.Sprintf("invalid bitfiled %v", b))
}
return (i[b.Word] >> (32 - 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 [2]uint32) int32 {
u := int32(b.Parse(i))
return u << (32 - b.Bits) >> (32 - b.Bits)
}
// BitFields is a series of BitFields representing a single number.
type BitFields []BitField
func (bs BitFields) String() string {
ss := make([]string, len(bs))
for i, bf := range bs {
ss[i] = bf.String()
}
return fmt.Sprintf("<%s>", strings.Join(ss, "|"))
}
func (bs *BitFields) Append(b BitField) {
*bs = append(*bs, b)
}
// parse extracts the bitfields from i, concatenate them and return the result
// as an unsigned integer and the total length of all the bitfields.
// parse will panic if any bitfield in b is invalid, but it doesn't check if
// the sequence of bitfields is reasonable.
func (bs BitFields) parse(i [2]uint32) (u uint64, Bits uint8) {
for _, b := range bs {
u = (uint64(u) << b.Bits) | uint64(b.Parse(i))
Bits += b.Bits
}
return u, Bits
}
// Parse extracts the bitfields from i, concatenate them and return the result
// as an unsigned integer. Parse will panic if any bitfield in b is invalid.
func (bs BitFields) Parse(i [2]uint32) uint64 {
u, _ := bs.parse(i)
return u
}
// Parse extracts the bitfields from i, concatenate them and return the result
// as a signed integer. Parse will panic if any bitfield in b is invalid.
func (bs BitFields) ParseSigned(i [2]uint32) int64 {
u, l := bs.parse(i)
return int64(u) << (64 - l) >> (64 - l)
}
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