forked from mirrors/gotosocial
126 lines
3.1 KiB
Go
126 lines
3.1 KiB
Go
// Copyright 2019 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package s390x
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import (
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"fmt"
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)
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// CCMask represents a 4-bit condition code mask. Bits that
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// are not part of the mask should be 0.
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//
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// Condition code masks represent the 4 possible values of
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// the 2-bit condition code as individual bits. Since IBM Z
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// is a big-endian platform bits are numbered from left to
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// right. The lowest value, 0, is represented by 8 (0b1000)
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// and the highest value, 3, is represented by 1 (0b0001).
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//
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// Note that condition code values have different semantics
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// depending on the instruction that set the condition code.
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// The names given here assume that the condition code was
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// set by an integer or floating point comparison. Other
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// instructions may use these same codes to indicate
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// different results such as a carry or overflow.
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type CCMask uint8
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const (
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Never CCMask = 0 // no-op
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// 1-bit masks
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Equal CCMask = 1 << 3
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Less CCMask = 1 << 2
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Greater CCMask = 1 << 1
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Unordered CCMask = 1 << 0
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// 2-bit masks
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EqualOrUnordered CCMask = Equal | Unordered // not less and not greater
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LessOrEqual CCMask = Less | Equal // ordered and not greater
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LessOrGreater CCMask = Less | Greater // ordered and not equal
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LessOrUnordered CCMask = Less | Unordered // not greater and not equal
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GreaterOrEqual CCMask = Greater | Equal // ordered and not less
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GreaterOrUnordered CCMask = Greater | Unordered // not less and not equal
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// 3-bit masks
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NotEqual CCMask = Always ^ Equal
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NotLess CCMask = Always ^ Less
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NotGreater CCMask = Always ^ Greater
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NotUnordered CCMask = Always ^ Unordered
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// 4-bit mask
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Always CCMask = Equal | Less | Greater | Unordered
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// useful aliases
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Carry CCMask = GreaterOrUnordered
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NoCarry CCMask = LessOrEqual
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Borrow CCMask = NoCarry
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NoBorrow CCMask = Carry
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)
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// Inverse returns the complement of the condition code mask.
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func (c CCMask) Inverse() CCMask {
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return c ^ Always
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}
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// ReverseComparison swaps the bits at 0b0100 and 0b0010 in the mask,
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// reversing the behavior of greater than and less than conditions.
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func (c CCMask) ReverseComparison() CCMask {
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r := c & EqualOrUnordered
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if c&Less != 0 {
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r |= Greater
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}
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if c&Greater != 0 {
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r |= Less
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}
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return r
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}
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func (c CCMask) String() string {
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switch c {
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// 0-bit mask
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case Never:
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return "Never"
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// 1-bit masks
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case Equal:
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return "Equal"
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case Less:
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return "Less"
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case Greater:
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return "Greater"
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case Unordered:
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return "Unordered"
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// 2-bit masks
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case EqualOrUnordered:
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return "EqualOrUnordered"
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case LessOrEqual:
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return "LessOrEqual"
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case LessOrGreater:
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return "LessOrGreater"
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case LessOrUnordered:
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return "LessOrUnordered"
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case GreaterOrEqual:
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return "GreaterOrEqual"
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case GreaterOrUnordered:
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return "GreaterOrUnordered"
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// 3-bit masks
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case NotEqual:
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return "NotEqual"
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case NotLess:
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return "NotLess"
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case NotGreater:
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return "NotGreater"
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case NotUnordered:
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return "NotUnordered"
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// 4-bit mask
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case Always:
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return "Always"
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}
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// invalid
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return fmt.Sprintf("Invalid (%#x)", c)
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}
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