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fq/pkg/bitio/reversebytes64.go

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bitio,decode: Refactor bitio usage and make buffer slicing more correct Remove bitio.Buffer layer. bitio.Buffer was a kitchen sink layer with helpers now it's just a buffer and most functions have been moved to decode instead. bitio package now only have primitive types and functions simialar to standard library io and bytes packages. Make nearly eveything internally use bitio.Bit* interfaces so that slicing work correctly this will also make it possible to start experimenting with more complicated silcing helpers, ex things like: breplace(.header.bitrate; 123) to get a new buffer with bitrate changed.
2022-01-24 23:21:48 +03:00
package bitio
import "fmt"
bitio,doc: Even more cleanup
2022-02-09 03:22:51 +03:00
// ReverseBytes64 reverses the bytes part of the lowest nBits.
// Similar to bits.ReverseBytes64 but only rotates the lowest bytes and rest of bytes will be zero.
bitio,decode: Refactor bitio usage and make buffer slicing more correct Remove bitio.Buffer layer. bitio.Buffer was a kitchen sink layer with helpers now it's just a buffer and most functions have been moved to decode instead. bitio package now only have primitive types and functions simialar to standard library io and bytes packages. Make nearly eveything internally use bitio.Bit* interfaces so that slicing work correctly this will also make it possible to start experimenting with more complicated silcing helpers, ex things like: breplace(.header.bitrate; 123) to get a new buffer with bitrate changed.
2022-01-24 23:21:48 +03:00
func ReverseBytes64(nBits int, n uint64) uint64 {
switch {
case nBits <= 8:
return n
case nBits <= 16:
return n&0xff00>>8 | n&0xff<<8
case nBits <= 24:
return n&0xff<<16 | n&0xff00 | n&0xff0000>>16
case nBits <= 32:
return n&0xff<<24 | n&0xff00<<8 | n&0xff0000>>8 | n&0xff000000>>24
case nBits <= 40:
return n&0xff<<32 | n&0xff00<<16 | n&0xff0000 | n&0xff000000>>16 | n&0xff00000000>>32
case nBits <= 48:
return n&0xff<<40 | n&0xff00<<24 | n&0xff0000<<8 | n&0xff000000>>8 | n&0xff00000000>>24 | n&0xff0000000000>>40
case nBits <= 56:
return n&0xff<<48 | n&0xff00<<32 | n&0xff0000<<16 | n&0xff000000 | n&0xff00000000>>16 | n&0xff0000000000>>32 | n&0xff000000000000>>48
case nBits <= 64:
return n&0xff<<56 | n&0xff00<<40 | n&0xff0000<<24 | n&0xff000000<<8 | n&0xff00000000>>8 | n&0xff0000000000>>24 | n&0xff000000000000>>40 | n&0xff00000000000000>>56
default:
panic(fmt.Sprintf("unsupported bit length %d", nBits))
}
}
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