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40 lines
1.5 KiB
Go
40 lines
1.5 KiB
Go
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package bbolt
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import (
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"reflect"
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"unsafe"
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)
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func unsafeAdd(base unsafe.Pointer, offset uintptr) unsafe.Pointer {
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return unsafe.Pointer(uintptr(base) + offset)
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}
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func unsafeIndex(base unsafe.Pointer, offset uintptr, elemsz uintptr, n int) unsafe.Pointer {
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return unsafe.Pointer(uintptr(base) + offset + uintptr(n)*elemsz)
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}
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func unsafeByteSlice(base unsafe.Pointer, offset uintptr, i, j int) []byte {
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// See: https://github.com/golang/go/wiki/cgo#turning-c-arrays-into-go-slices
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//
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// This memory is not allocated from C, but it is unmanaged by Go's
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// garbage collector and should behave similarly, and the compiler
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// should produce similar code. Note that this conversion allows a
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// subslice to begin after the base address, with an optional offset,
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// while the URL above does not cover this case and only slices from
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// index 0. However, the wiki never says that the address must be to
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// the beginning of a C allocation (or even that malloc was used at
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// all), so this is believed to be correct.
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return (*[maxAllocSize]byte)(unsafeAdd(base, offset))[i:j:j]
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}
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// unsafeSlice modifies the data, len, and cap of a slice variable pointed to by
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// the slice parameter. This helper should be used over other direct
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// manipulation of reflect.SliceHeader to prevent misuse, namely, converting
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// from reflect.SliceHeader to a Go slice type.
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func unsafeSlice(slice, data unsafe.Pointer, len int) {
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s := (*reflect.SliceHeader)(slice)
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s.Data = uintptr(data)
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s.Cap = len
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s.Len = len
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}
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