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Slice structure definition

Type slice struct {

Array unsafe.Pointer

Len int

Cap int

}

Create slice

/ / maxSliceCap returns the maximum capacity for a slice.

Func maxSliceCap (elemsize uintptr) uintptr {

If elemsize

< uintptr(len(maxElems)) { return maxElems[elemsize] } return _MaxMem / elemsize } func makeslice(et *_type, len, cap int) slice { // NOTE: The len >

MaxElements check here is not strictly necessary

/ / but it produces a 'len out of range' error instead of a' cap out of range' error

/ / when someone does make ([] T, bignumber). 'cap out of range' is true too

/ / but since the cap is only being supplied implicitly, saying len is clearer.

/ / See issue 4085.

/ / calculate the maximum distributable length

MaxElements: = maxSliceCap (et.size)

If len

< 0 || uintptr(len) >

MaxElements {

Panic (errorString ("makeslice: len out of range"))

}

If cap

< len || uintptr(cap) >

MaxElements {

Panic (errorString ("makeslice: cap out of range"))

}

/ / assign continuous interval

P: = mallocgc (et.size*uintptr (cap), et, true)

Return slice {p, len, cap}

}

Slice capacity expansion

/ / cap target capacity

Func growslice (et * _ type, old slice, cap int) slice {

If et.size = = 0 {

If cap

< old.cap { panic(errorString("growslice: cap out of range")) } // append should not create a slice with nil pointer but non-zero len. // We assume that append doesn't need to preserve old.array in this case. return slice{unsafe.Pointer(&zerobase), old.len, cap} } newcap := old.cap doublecap := newcap + newcap if cap >

Doublecap {

Newcap = cap

} else {

/ / less than 1024 and expand the capacity

If old.len

< 1024 { newcap = doublecap } else { // 大于1024，*1.25 for newcap < cap { newcap += newcap / 4 } } } var lenmem, newlenmem, capmem uintptr const ptrSize = unsafe.Sizeof((*byte)(nil)) switch et.size { case 1: lenmem = uintptr(old.len) newlenmem = uintptr(cap) capmem = roundupsize(uintptr(newcap)) newcap = int(capmem) case ptrSize: lenmem = uintptr(old.len) * ptrSize newlenmem = uintptr(cap) * ptrSize capmem = roundupsize(uintptr(newcap) * ptrSize) newcap = int(capmem / ptrSize) default: lenmem = uintptr(old.len) * et.size newlenmem = uintptr(cap) * et.size capmem = roundupsize(uintptr(newcap) * et.size) newcap = int(capmem / et.size) } if cap < old.cap || uintptr(newcap) >

MaxSliceCap (et.size) {

Panic (errorString ("growslice: cap out of range"))

}

Var p unsafe.Pointer

If et.kind&kindNoPointers! = 0 {

P = mallocgc (capmem, nil, false)

Memmove (p, old.array, lenmem)

/ / The append () that calls growslice is going to overwrite from old.len to cap (which will be the new length)

/ / Only clear the part that will not be overwritten.

MemclrNoHeapPointers (add (p, newlenmem), capmem-newlenmem)

} else {

/ / Note: can't use rawmem (which avoids zeroing of memory), because then GC can scan uninitialized memory.

P = mallocgc (capmem, et, true)

If! writeBarrier.enabled {

Memmove (p, old.array, lenmem)

} else {

For I: = uintptr (0); I < lenmem; I + = et.size {

Typedmemmove (et, add (p, I), add (old.array, I))

}

}

}

/ / New slice

Return slice {p, old.len, newcap}

}

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