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utils.go
60 lines (54 loc) · 1.24 KB
/
utils.go
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package quicklist
import (
"encoding/binary"
"math/bits"
"slices"
"unsafe"
)
func appendUvarint(b []byte, n int, reverse bool) []byte {
if !reverse {
return binary.AppendUvarint(b, uint64(n))
}
before := len(b)
b = binary.AppendUvarint(b, uint64(n))
after := len(b)
if after-before > 1 {
slices.Reverse(b[before:])
}
return b
}
// uvarintReverse is the reverse version from binary.Uvarint.
func uvarintReverse(buf []byte) (uint64, int) {
var x uint64
var s uint
for i := range buf {
b := buf[len(buf)-1-i]
if i == binary.MaxVarintLen64 {
return 0, -(i + 1) // overflow
}
if b < 0x80 {
if i == binary.MaxVarintLen64-1 && b > 1 {
return 0, -(i + 1) // overflow
}
return x | uint64(b)<<s, i + 1
}
x |= uint64(b&0x7f) << s
s += 7
}
return 0, 0
}
// SizeUvarint
// See https://go-review.googlesource.com/c/go/+/572196/1/src/encoding/binary/varint.go#174
func SizeUvarint(x uint64) int {
return int(9*uint32(bits.Len64(x))+64) / 64
}
func s2b(str *string) []byte {
strHeader := (*[2]uintptr)(unsafe.Pointer(str))
byteSliceHeader := [3]uintptr{
strHeader[0], strHeader[1], strHeader[1],
}
return *(*[]byte)(unsafe.Pointer(&byteSliceHeader))
}
func b2s(b []byte) string {
return *(*string)(unsafe.Pointer(&b))
}