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 // sizeToClass(0 <= n <= MaxSmallSize) returns the size class, 13 // 1 <= sizeclass < NumSizeClasses, for n. 14 // Size class 0 is reserved to mean "not small". 15 // 16 // The sizeToClass lookup is implemented using two arrays, 17 // one mapping sizes <= 1024 to their class and one mapping 18 // sizes >= 1024 and <= MaxSmallSize to their class. 19 // All objects are 8-aligned, so the first array is indexed by 20 // the size divided by 8 (rounded up). Objects >= 1024 bytes 21 // are 128-aligned, so the second array is indexed by the 22 // size divided by 128 (rounded up). The arrays are constants 23 // in sizeclass.go generated by mksizeclass.go. 24 func sizeToClass(size uint32) uint32 { 25 if size > _MaxSmallSize { 26 throw("invalid size") 27 } 28 if size > smallSizeMax-8 { 29 return uint32(size_to_class128[(size-smallSizeMax+largeSizeDiv-1)/largeSizeDiv]) 30 } 31 return uint32(size_to_class8[(size+smallSizeDiv-1)/smallSizeDiv]) 32 } 33 34 // Returns size of the memory block that mallocgc will allocate if you ask for the size. 35 func roundupsize(size uintptr) uintptr { 36 if size < _MaxSmallSize { 37 if size <= smallSizeMax-8 { 38 return uintptr(class_to_size[size_to_class8[(size+smallSizeDiv-1)/smallSizeDiv]]) 39 } else { 40 return uintptr(class_to_size[size_to_class128[(size-smallSizeMax+largeSizeDiv-1)/largeSizeDiv]]) 41 } 42 } 43 if size+_PageSize < size { 44 return size 45 } 46 return round(size, _PageSize) 47 } 48
