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Fix Utils.decodeMPI and add a Utils.encodeMPI

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Matt Corallo 2012-08-02 18:00:04 +02:00 committed by Mike Hearn
parent 61ed962e63
commit e5c88cda8b
2 changed files with 59 additions and 7 deletions
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1
core/src/main/java/com/google/bitcoin/core/Script.java
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@ -612,6 +612,7 @@ public class Script {
/**
* Writes out the given byte buffer to the output stream with the correct opcode prefix
* To write an integer call writeBytes(out, Utils.reverseBytes(Utils.encodeMPI(val, false)));
*/
static void writeBytes(OutputStream os, byte[] buf) throws IOException {
if (buf.length < OP_PUSHDATA1) {

61
core/src/main/java/com/google/bitcoin/core/Utils.java
View File

@ -323,13 +323,64 @@ public class Utils {
/**
* MPI encoded numbers are produced by the OpenSSL BN_bn2mpi function. They consist of
* a 4 byte big endian length field, followed by the stated number of bytes representing
* the number in big endian format.
* the number in big endian format (with a sign bit).
* @param hasLength can be set to false if the given array is missing the 4 byte length field
*/
static BigInteger decodeMPI(byte[] mpi) {
static BigInteger decodeMPI(byte[] mpi, boolean hasLength) {
byte[] buf;
if (hasLength) {
int length = (int) readUint32BE(mpi, 0);
byte[] buf = new byte[length];
buf = new byte[length];
System.arraycopy(mpi, 4, buf, 0, length);
return new BigInteger(buf);
} else
buf = mpi;
if (buf.length == 0)
return BigInteger.ZERO;
boolean isNegative = (buf[0] & 0x80) == 0x80;
if (isNegative)
buf[0] &= 0x7f;
BigInteger result = new BigInteger(buf);
return isNegative ? result.negate() : result;
}
/**
* MPI encoded numbers are produced by the OpenSSL BN_bn2mpi function. They consist of
* a 4 byte big endian length field, followed by the stated number of bytes representing
* the number in big endian format (with a sign bit).
* @param hasLength indicates whether the 4 byte length field should be included
*/
static byte[] encodeMPI(BigInteger value, boolean includeLength) {
if (value.equals(BigInteger.ZERO)) {
if (!includeLength)
return new byte[] {};
else
return new byte[] {0x00, 0x00, 0x00, 0x00};
}
boolean isNegative = value.compareTo(BigInteger.ZERO) < 0;
if (isNegative)
value = value.negate();
byte[] array = value.toByteArray();
int length = array.length;
if ((array[0] & 0x80) == 0x80)
length++;
if (includeLength) {
byte[] result = new byte[length + 4];
System.arraycopy(array, 0, result, length - array.length + 3, array.length);
uint32ToByteArrayBE(length, result, 0);
if (isNegative)
result[4] |= 0x80;
return result;
} else {
byte[] result;
if (length != array.length) {
result = new byte[length];
System.arraycopy(array, 0, result, 1, array.length);
}else
result = array;
if (isNegative)
result[0] |= 0x80;
return result;
}
}
// The representation of nBits uses another home-brew encoding, as a way to represent a large
@ -341,7 +392,7 @@ public class Utils {
if (size >= 1) bytes[4] = (byte) ((compact >> 16) & 0xFF);
if (size >= 2) bytes[5] = (byte) ((compact >> 8) & 0xFF);
if (size >= 3) bytes[6] = (byte) ((compact >> 0) & 0xFF);
return decodeMPI(bytes);
return decodeMPI(bytes, true);
}
/**