81 lines
1.8 KiB
Go
81 lines
1.8 KiB
Go
package asm
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// Metadata contains metadata about an instruction.
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type Metadata struct {
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head *metaElement
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}
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type metaElement struct {
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next *metaElement
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key, value interface{}
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}
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// Find the element containing key.
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//
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// Returns nil if there is no such element.
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func (m *Metadata) find(key interface{}) *metaElement {
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for e := m.head; e != nil; e = e.next {
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if e.key == key {
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return e
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}
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}
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return nil
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}
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// Remove an element from the linked list.
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//
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// Copies as many elements of the list as necessary to remove r, but doesn't
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// perform a full copy.
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func (m *Metadata) remove(r *metaElement) {
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current := &m.head
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for e := m.head; e != nil; e = e.next {
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if e == r {
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// We've found the element we want to remove.
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*current = e.next
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// No need to copy the tail.
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return
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}
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// There is another element in front of the one we want to remove.
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// We have to copy it to be able to change metaElement.next.
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cpy := &metaElement{key: e.key, value: e.value}
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*current = cpy
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current = &cpy.next
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}
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}
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// Set a key to a value.
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//
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// If value is nil, the key is removed. Avoids modifying old metadata by
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// copying if necessary.
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func (m *Metadata) Set(key, value interface{}) {
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if e := m.find(key); e != nil {
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if e.value == value {
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// Key is present and the value is the same. Nothing to do.
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return
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}
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// Key is present with a different value. Create a copy of the list
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// which doesn't have the element in it.
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m.remove(e)
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}
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// m.head is now a linked list that doesn't contain key.
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if value == nil {
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return
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}
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m.head = &metaElement{key: key, value: value, next: m.head}
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}
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// Get the value of a key.
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//
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// Returns nil if no value with the given key is present.
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func (m *Metadata) Get(key interface{}) interface{} {
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if e := m.find(key); e != nil {
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return e.value
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}
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return nil
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}
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