65 lines
1.5 KiB
Go
65 lines
1.5 KiB
Go
package varint
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import (
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"encoding/binary"
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"math"
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)
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// MaxVarintLen is the maximum number of bytes required to encode a varint
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// number.
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const MaxVarintLen = 10
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// Encode encodes the given value to varint format.
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func Encode(b []byte, value int64) int {
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// 111111xx Byte-inverted negative two bit number (~xx)
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if value <= -1 && value >= -4 {
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b[0] = 0xFC | byte(^value&0xFF)
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return 1
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}
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// 111110__ + varint Negative recursive varint
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if value < 0 {
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b[0] = 0xF8
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return 1 + Encode(b[1:], -value)
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}
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// 0xxxxxxx 7-bit positive number
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if value <= 0x7F {
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b[0] = byte(value)
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return 1
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}
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// 10xxxxxx + 1 byte 14-bit positive number
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if value <= 0x3FFF {
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b[0] = byte(((value >> 8) & 0x3F) | 0x80)
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b[1] = byte(value & 0xFF)
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return 2
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}
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// 110xxxxx + 2 bytes 21-bit positive number
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if value <= 0x1FFFFF {
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b[0] = byte((value>>16)&0x1F | 0xC0)
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b[1] = byte((value >> 8) & 0xFF)
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b[2] = byte(value & 0xFF)
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return 3
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}
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// 1110xxxx + 3 bytes 28-bit positive number
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if value <= 0xFFFFFFF {
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b[0] = byte((value>>24)&0xF | 0xE0)
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b[1] = byte((value >> 16) & 0xFF)
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b[2] = byte((value >> 8) & 0xFF)
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b[3] = byte(value & 0xFF)
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return 4
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}
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// 111100__ + int (32-bit) 32-bit positive number
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if value <= math.MaxInt32 {
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b[0] = 0xF0
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binary.BigEndian.PutUint32(b[1:], uint32(value))
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return 5
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}
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// 111101__ + long (64-bit) 64-bit number
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if value <= math.MaxInt64 {
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b[0] = 0xF4
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binary.BigEndian.PutUint64(b[1:], uint64(value))
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return 9
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}
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return 0
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}
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