104 lines
2.8 KiB
Go
104 lines
2.8 KiB
Go
// Copyright (c) 2024-2026 Lethean Contributors
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// SPDX-License-Identifier: EUPL-1.2
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package levin
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import (
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"encoding/binary"
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core "dappco.re/go/core"
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)
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// Size-mark bits occupying the two lowest bits of the first byte.
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const (
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varintMask = 0x03
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varintMark1 = 0x00 // 1 byte, max 63
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varintMark2 = 0x01 // 2 bytes, max 16,383
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varintMark4 = 0x02 // 4 bytes, max 1,073,741,823
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varintMark8 = 0x03 // 8 bytes, max 4,611,686,018,427,387,903
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varintMax1 = 63
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varintMax2 = 16_383
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varintMax4 = 1_073_741_823
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varintMax8 = 4_611_686_018_427_387_903
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)
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// ErrorVarintTruncated is returned when the buffer is too short.
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var ErrorVarintTruncated = core.E("levin", "truncated varint", nil)
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// Deprecated: use ErrorVarintTruncated.
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var ErrVarintTruncated = ErrorVarintTruncated
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// ErrorVarintOverflow is returned when the value is too large to encode.
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var ErrorVarintOverflow = core.E("levin", "varint overflow", nil)
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// Deprecated: use ErrorVarintOverflow.
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var ErrVarintOverflow = ErrorVarintOverflow
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// PackVarint encodes v using the epee portable-storage varint scheme.
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// The low two bits of the first byte indicate the total encoded width;
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// the remaining bits carry the value in little-endian order.
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//
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// encoded := PackVarint(42)
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func PackVarint(v uint64) []byte {
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switch {
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case v <= varintMax1:
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return []byte{byte((v << 2) | varintMark1)}
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case v <= varintMax2:
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raw := uint16((v << 2) | varintMark2)
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buf := make([]byte, 2)
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binary.LittleEndian.PutUint16(buf, raw)
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return buf
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case v <= varintMax4:
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raw := uint32((v << 2) | varintMark4)
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buf := make([]byte, 4)
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binary.LittleEndian.PutUint32(buf, raw)
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return buf
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default:
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raw := (v << 2) | varintMark8
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buf := make([]byte, 8)
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binary.LittleEndian.PutUint64(buf, raw)
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return buf
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}
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}
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// UnpackVarint decodes one epee portable-storage varint from buf.
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// It returns the decoded value, the number of bytes consumed, and any error.
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//
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// value, err := UnpackVarint(data)
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func UnpackVarint(buf []byte) (value uint64, bytesConsumed int, err error) {
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if len(buf) == 0 {
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return 0, 0, ErrorVarintTruncated
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}
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mark := buf[0] & varintMask
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switch mark {
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case varintMark1:
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value = uint64(buf[0]) >> 2
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return value, 1, nil
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case varintMark2:
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if len(buf) < 2 {
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return 0, 0, ErrorVarintTruncated
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}
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raw := binary.LittleEndian.Uint16(buf[:2])
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value = uint64(raw) >> 2
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return value, 2, nil
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case varintMark4:
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if len(buf) < 4 {
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return 0, 0, ErrorVarintTruncated
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}
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raw := binary.LittleEndian.Uint32(buf[:4])
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value = uint64(raw) >> 2
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return value, 4, nil
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case varintMark8:
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if len(buf) < 8 {
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return 0, 0, ErrorVarintTruncated
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}
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raw := binary.LittleEndian.Uint64(buf[:8])
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value = raw >> 2
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return value, 8, nil
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default:
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// Unreachable — mark is masked to 2 bits.
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return 0, 0, ErrorVarintTruncated
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}
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}
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