Function MakeScriptNum

txscript/scriptnum.go:198–238

MakeScriptNum interprets the passed serialized bytes as an encoded integer and returns the result as a script number. Since the consensus rules dictate that serialized bytes interpreted as ints are only allowed to be in the range determined by a maximum number of bytes, on a per opcode basis, an er

(v []byte, requireMinimal bool, scriptNumLen int)

//
// See the Bytes function documentation for example encodings.
func MakeScriptNum(v []byte, requireMinimal bool, scriptNumLen int) (scriptNum, error) {
	// Interpreting data requires that it is not larger than
	// the passed scriptNumLen value.
	if len(v) > scriptNumLen {
		str := fmt.Sprintf("numeric value encoded as %x is %d bytes "+
			"which exceeds the max allowed of %d", v, len(v),
			scriptNumLen)
		return 0, scriptError(ErrNumberTooBig, str)
	}

	// Enforce minimal encoded if requested.
	if requireMinimal {
		if err := checkMinimalDataEncoding(v); err != nil {
			return 0, err
		}
	}

	// Zero is encoded as an empty byte slice.
	if len(v) == 0 {
		return 0, nil
	}

	// Decode from little endian.
	var result int64
	for i, val := range v {
		result |= int64(val) << uint8(8*i)
	}

	// When the most significant byte of the input bytes has the sign bit
	// set, the result is negative.  So, remove the sign bit from the result
	// and make it negative.
	if v[len(v)-1]&0x80 != 0 {
		// The maximum length of v has already been determined to be 4
		// above, so uint8 is enough to cover the max possible shift
		// value of 24.
		result &= ^(int64(0x80) << uint8(8*(len(v)-1)))
		return scriptNum(-result), nil
	}

	return scriptNum(result), nil
}