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package danger
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import (
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	"fmt"
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	"reflect"
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	"unsafe"
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)
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const maxInt = uintptr(int(^uint(0) >> 1))
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func SubsliceOffset(data []byte, subslice []byte) int {
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	datap := (*reflect.SliceHeader)(unsafe.Pointer(&data))
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	hlp := (*reflect.SliceHeader)(unsafe.Pointer(&subslice))
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	if hlp.Data < datap.Data {
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		panic(fmt.Errorf("subslice address (%d) is before data address (%d)", hlp.Data, datap.Data))
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	}
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	offset := hlp.Data - datap.Data
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	if offset > maxInt {
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		panic(fmt.Errorf("slice offset larger than int (%d)", offset))
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	}
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	intoffset := int(offset)
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	if intoffset > datap.Len {
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		panic(fmt.Errorf("slice offset (%d) is farther than data length (%d)", intoffset, datap.Len))
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	}
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	if intoffset+hlp.Len > datap.Len {
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		panic(fmt.Errorf("slice ends (%d+%d) is farther than data length (%d)", intoffset, hlp.Len, datap.Len))
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	}
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	return intoffset
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}
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func BytesRange(start []byte, end []byte) []byte {
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	if start == nil || end == nil {
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		panic("cannot call BytesRange with nil")
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	}
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	startp := (*reflect.SliceHeader)(unsafe.Pointer(&start))
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	endp := (*reflect.SliceHeader)(unsafe.Pointer(&end))
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	if startp.Data > endp.Data {
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		panic(fmt.Errorf("start pointer address (%d) is after end pointer address (%d)", startp.Data, endp.Data))
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	}
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	l := startp.Len
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	endLen := int(endp.Data-startp.Data) + endp.Len
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	if endLen > l {
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		l = endLen
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	}
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	if l > startp.Cap {
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		panic(fmt.Errorf("range length is larger than capacity"))
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	}
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	return start[:l]
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}
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func Stride(ptr unsafe.Pointer, size uintptr, offset int) unsafe.Pointer {
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	// TODO: replace with unsafe.Add when Go 1.17 is released
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	//   https://github.com/golang/go/issues/40481
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	return unsafe.Pointer(uintptr(ptr) + uintptr(int(size)*offset))
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}
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