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// Copyright 2009 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.
//go:build goexperiment.allocheaders
// Malloc small size classes.
//
// See malloc.go for overview.
// See also mksizeclasses.go for how we decide what size classes to use.
package runtime
// Returns size of the memory block that mallocgc will allocate if you ask for the size,
// minus any inline space for metadata.
func roundupsize(size uintptr, noscan bool) (reqSize uintptr) {
reqSize = size
if reqSize <= maxSmallSize-mallocHeaderSize {
// Small object.
if !noscan && reqSize > minSizeForMallocHeader { // !noscan && !heapBitsInSpan(reqSize)
reqSize += mallocHeaderSize
}
// (reqSize - size) is either mallocHeaderSize or 0. We need to subtract mallocHeaderSize
// from the result if we have one, since mallocgc will add it back in.
if reqSize <= smallSizeMax-8 {
return uintptr(class_to_size[size_to_class8[divRoundUp(reqSize, smallSizeDiv)]]) - (reqSize - size)
}
return uintptr(class_to_size[size_to_class128[divRoundUp(reqSize-smallSizeMax, largeSizeDiv)]]) - (reqSize - size)
}
// Large object. Align reqSize up to the next page. Check for overflow.
reqSize += pageSize - 1
if reqSize < size {
return size
}
return reqSize &^ (pageSize - 1)
}
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