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runtime: use sys.PtrSize in growslice

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Minor cleanup.

Change-Id: I4175de392969bb6408081a75cebdaeadcef1e68c
Reviewed-on: https://go-review.googlesource.com/108576
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Josh Bleecher Snyder 2018-04-20 10:22:54 -07:00
parent 566e3e074c
commit 37dd7cd040
1 changed files with 8 additions and 9 deletions
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17
src/runtime/slice.go
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@ -128,10 +128,9 @@ func growslice(et *_type, old slice, cap int) slice {
var overflow bool
var lenmem, newlenmem, capmem uintptr
const ptrSize = unsafe.Sizeof((*byte)(nil))
// Specialize for common values of et.size.
// For 1 we don't need any division/multiplication.
// For ptrSize, compiler will optimize division/multiplication into a shift by a constant.
// For sys.PtrSize, compiler will optimize division/multiplication into a shift by a constant.
// For powers of 2, use a variable shift.
switch {
case et.size == 1:
@ -140,15 +139,15 @@ func growslice(et *_type, old slice, cap int) slice {
capmem = roundupsize(uintptr(newcap))
overflow = uintptr(newcap) > maxAlloc
newcap = int(capmem)
case et.size == ptrSize:
lenmem = uintptr(old.len) * ptrSize
newlenmem = uintptr(cap) * ptrSize
capmem = roundupsize(uintptr(newcap) * ptrSize)
overflow = uintptr(newcap) > maxAlloc/ptrSize
newcap = int(capmem / ptrSize)
case et.size == sys.PtrSize:
lenmem = uintptr(old.len) * sys.PtrSize
newlenmem = uintptr(cap) * sys.PtrSize
capmem = roundupsize(uintptr(newcap) * sys.PtrSize)
overflow = uintptr(newcap) > maxAlloc/sys.PtrSize
newcap = int(capmem / sys.PtrSize)
case isPowerOfTwo(et.size):
var shift uintptr
if ptrSize == 8 {
if sys.PtrSize == 8 {
// Mask shift for better code generation.
shift = uintptr(sys.Ctz64(uint64(et.size))) & 63
} else {