1 files changed, 115 insertions, 0 deletions
diff --git a/src/cmd/internal/obj/s390x/rotate.go b/src/cmd/internal/obj/s390x/rotate.go
new file mode 100644
index 0000000..388bd40
--- /dev/null
+++ b/src/cmd/internal/obj/s390x/rotate.go
@@ -0,0 +1,115 @@
+// Copyright 2019 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 s390x
+
+import (
+	"math/bits"
+)
+
+// RotateParams represents the immediates required for a "rotate
+// then ... selected bits instruction".
+//
+// The Start and End values are the indexes that represent
+// the masked region. They are inclusive and are in big-
+// endian order (bit 0 is the MSB, bit 63 is the LSB). They
+// may wrap around.
+//
+// Some examples:
+//
+// Masked region             | Start | End
+// --------------------------+-------+----
+// 0x00_00_00_00_00_00_00_0f | 60    | 63
+// 0xf0_00_00_00_00_00_00_00 | 0     | 3
+// 0xf0_00_00_00_00_00_00_0f | 60    | 3
+//
+// The Amount value represents the amount to rotate the
+// input left by. Note that this rotation is performed
+// before the masked region is used.
+type RotateParams struct {
+	Start  uint8 // big-endian start bit index [0..63]
+	End    uint8 // big-endian end bit index [0..63]
+	Amount uint8 // amount to rotate left
+}
+
+// NewRotateParams creates a set of parameters representing a
+// rotation left by the amount provided and a selection of the bits
+// between the provided start and end indexes (inclusive).
+//
+// The start and end indexes and the rotation amount must all
+// be in the range 0-63 inclusive or this function will panic.
+func NewRotateParams(start, end, amount uint8) RotateParams {
+	if start&^63 != 0 {
+		panic("start out of bounds")
+	}
+	if end&^63 != 0 {
+		panic("end out of bounds")
+	}
+	if amount&^63 != 0 {
+		panic("amount out of bounds")
+	}
+	return RotateParams{
+		Start:  start,
+		End:    end,
+		Amount: amount,
+	}
+}
+
+// RotateLeft generates a new set of parameters with the rotation amount
+// increased by the given value. The selected bits are left unchanged.
+func (r RotateParams) RotateLeft(amount uint8) RotateParams {
+	r.Amount += amount
+	r.Amount &= 63
+	return r
+}
+
+// OutMask provides a mask representing the selected bits.
+func (r RotateParams) OutMask() uint64 {
+	// Note: z must be unsigned for bootstrap compiler
+	z := uint8(63-r.End+r.Start) & 63 // number of zero bits in mask
+	return bits.RotateLeft64(^uint64(0)<<z, -int(r.Start))
+}
+
+// InMask provides a mask representing the selected bits relative
+// to the source value (i.e. pre-rotation).
+func (r RotateParams) InMask() uint64 {
+	return bits.RotateLeft64(r.OutMask(), -int(r.Amount))
+}
+
+// OutMerge tries to generate a new set of parameters representing
+// the intersection between the selected bits and the provided mask.
+// If the intersection is unrepresentable (0 or not contiguous) nil
+// will be returned.
+func (r RotateParams) OutMerge(mask uint64) *RotateParams {
+	mask &= r.OutMask()
+	if mask == 0 {
+		return nil
+	}
+
+	// normalize the mask so that the set bits are left aligned
+	o := bits.LeadingZeros64(^mask)
+	mask = bits.RotateLeft64(mask, o)
+	z := bits.LeadingZeros64(mask)
+	mask = bits.RotateLeft64(mask, z)
+
+	// check that the normalized mask is contiguous
+	l := bits.LeadingZeros64(^mask)
+	if l+bits.TrailingZeros64(mask) != 64 {
+		return nil
+	}
+
+	// update start and end positions (rotation amount remains the same)
+	r.Start = uint8(o+z) & 63
+	r.End = (r.Start + uint8(l) - 1) & 63
+	return &r
+}
+
+// InMerge tries to generate a new set of parameters representing
+// the intersection between the selected bits and the provided mask
+// as applied to the source value (i.e. pre-rotation).
+// If the intersection is unrepresentable (0 or not contiguous) nil
+// will be returned.
+func (r RotateParams) InMerge(mask uint64) *RotateParams {
+	return r.OutMerge(bits.RotateLeft64(mask, int(r.Amount)))
+}