Source file src/runtime/msize.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Malloc small size classes.
     6  //
     7  // See malloc.go for overview.
     8  // See also mksizeclasses.go for how we decide what size classes to use.
     9  
    10  package runtime
    11  
    12  // Returns size of the memory block that mallocgc will allocate if you ask for the size,
    13  // minus any inline space for metadata.
    14  func roundupsize(size uintptr, noscan bool) (reqSize uintptr) {
    15  	reqSize = size
    16  	if reqSize <= maxSmallSize-mallocHeaderSize {
    17  		// Small object.
    18  		if !noscan && reqSize > minSizeForMallocHeader { // !noscan && !heapBitsInSpan(reqSize)
    19  			reqSize += mallocHeaderSize
    20  		}
    21  		// (reqSize - size) is either mallocHeaderSize or 0. We need to subtract mallocHeaderSize
    22  		// from the result if we have one, since mallocgc will add it back in.
    23  		if reqSize <= smallSizeMax-8 {
    24  			return uintptr(class_to_size[size_to_class8[divRoundUp(reqSize, smallSizeDiv)]]) - (reqSize - size)
    25  		}
    26  		return uintptr(class_to_size[size_to_class128[divRoundUp(reqSize-smallSizeMax, largeSizeDiv)]]) - (reqSize - size)
    27  	}
    28  	// Large object. Align reqSize up to the next page. Check for overflow.
    29  	reqSize += pageSize - 1
    30  	if reqSize < size {
    31  		return size
    32  	}
    33  	return reqSize &^ (pageSize - 1)
    34  }
    35  

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