41 lines
1.0 KiB
Go
41 lines
1.0 KiB
Go
// Copyright (C) 2018 Storj Labs, Inc.
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// See LICENSE for copying information.
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package eestream
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import "math/big"
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// incrementBytes takes a byte slice buf and treats it like a big-endian
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// encoded unsigned integer. it adds amount to it (which must be nonnegative)
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// in place. if rollover happens (the most significant bytes don't fit
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// anymore), truncated is true.
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func incrementBytes(buf []byte, amount int64) (truncated bool,
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err error) {
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if amount < 0 {
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return false, Error.New("amount was negative")
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}
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// use math/big for the actual incrementing
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var val big.Int
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val.SetBytes(buf)
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val.Add(&val, big.NewInt(amount))
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data := val.Bytes()
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// we went past the available memory. truncate the most significant bytes
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// off
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if len(data) > len(buf) {
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data = data[len(data)-len(buf):]
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truncated = true
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}
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// math/big doesn't return leading 0 bytes so add them back if they're
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// missing
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for i := len(buf) - len(data) - 1; i >= 0; i-- {
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buf[i] = 0
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}
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// write the data out inplace
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copy(buf[len(buf)-len(data):], data[:])
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return truncated, nil
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}
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