1 // Copyright 2019 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 s390x
6 7 // RotateParams represents the immediates required for a "rotate
8 // then ... selected bits instruction".
9 //
10 // The Start and End values are the indexes that represent
11 // the masked region. They are inclusive and are in big-
12 // endian order (bit 0 is the MSB, bit 63 is the LSB). They
13 // may wrap around.
14 //
15 // Some examples:
16 //
17 // Masked region | Start | End
18 // --------------------------+-------+----
19 // 0x00_00_00_00_00_00_00_0f | 60 | 63
20 // 0xf0_00_00_00_00_00_00_00 | 0 | 3
21 // 0xf0_00_00_00_00_00_00_0f | 60 | 3
22 //
23 // The Amount value represents the amount to rotate the
24 // input left by. Note that this rotation is performed
25 // before the masked region is used.
26 type RotateParams struct {
27 Start uint8 // big-endian start bit index [0..63]
28 End uint8 // big-endian end bit index [0..63]
29 Amount uint8 // amount to rotate left
30 }
31 32 func NewRotateParams(start, end, amount int64) RotateParams {
33 if start&^63 != 0 {
34 panic("start out of bounds")
35 }
36 if end&^63 != 0 {
37 panic("end out of bounds")
38 }
39 if amount&^63 != 0 {
40 panic("amount out of bounds")
41 }
42 return RotateParams{
43 Start: uint8(start),
44 End: uint8(end),
45 Amount: uint8(amount),
46 }
47 }
48