41 lines
1.1 KiB
Go
41 lines
1.1 KiB
Go
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// Copyright 2009 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 runtime
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// nextslicecap computes the next appropriate slice length.
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func nextslicecap(newLen, oldCap int) int {
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newcap := oldCap
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doublecap := newcap + newcap
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if newLen > doublecap {
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return newLen
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}
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const threshold = 256
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if oldCap < threshold {
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return doublecap
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}
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for {
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// Transition from growing 2x for small slices
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// to growing 1.25x for large slices. This formula
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// gives a smooth-ish transition between the two.
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newcap += (newcap + 3*threshold) >> 2
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// We need to check `newcap >= newLen` and whether `newcap` overflowed.
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// newLen is guaranteed to be larger than zero, hence
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// when newcap overflows then `uint(newcap) > uint(newLen)`.
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// This allows to check for both with the same comparison.
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if uint(newcap) >= uint(newLen) {
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break
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}
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}
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// Set newcap to the requested cap when
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// the newcap calculation overflowed.
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if newcap <= 0 {
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return newLen
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}
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return newcap
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}
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