66 lines
1.2 KiB
Go
66 lines
1.2 KiB
Go
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// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
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// SPDX-License-Identifier: MIT
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package vp9
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import "errors"
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var errNotEnoughBits = errors.New("not enough bits")
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func hasSpace(buf []byte, pos int, n int) error {
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if n > ((len(buf) * 8) - pos) {
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return errNotEnoughBits
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}
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return nil
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}
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func readFlag(buf []byte, pos *int) (bool, error) {
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err := hasSpace(buf, *pos, 1)
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if err != nil {
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return false, err
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}
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return readFlagUnsafe(buf, pos), nil
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}
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func readFlagUnsafe(buf []byte, pos *int) bool {
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b := (buf[*pos>>0x03] >> (7 - (*pos & 0x07))) & 0x01
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*pos++
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return b == 1
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}
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func readBits(buf []byte, pos *int, n int) (uint64, error) {
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err := hasSpace(buf, *pos, n)
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if err != nil {
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return 0, err
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}
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return readBitsUnsafe(buf, pos, n), nil
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}
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func readBitsUnsafe(buf []byte, pos *int, n int) uint64 {
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res := 8 - (*pos & 0x07)
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if n < res {
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v := uint64((buf[*pos>>0x03] >> (res - n)) & (1<<n - 1))
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*pos += n
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return v
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}
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v := uint64(buf[*pos>>0x03] & (1<<res - 1))
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*pos += res
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n -= res
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for n >= 8 {
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v = (v << 8) | uint64(buf[*pos>>0x03])
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*pos += 8
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n -= 8
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}
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if n > 0 {
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v = (v << n) | uint64(buf[*pos>>0x03]>>(8-n))
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*pos += n
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}
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return v
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}
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