private static Expression BigIntConstant(BigInt value)
{
int ival;
if (value.AsInt32(out ival))
{
return(Expression.Call(
new Func <int, BigInt>(CompilerHelpers.CreateBigInt).GetMethodInfo(),
Constant(ival)
));
}
long lval;
if (value.AsInt64(out lval))
{
return(Expression.Call(
new Func <long, BigInt>(CompilerHelpers.CreateBigInt).GetMethodInfo(),
Constant(lval)
));
}
return(Expression.Call(
new Func <bool, byte[], BigInt>(CompilerHelpers.CreateBigInt).GetMethodInfo(),
Constant(value.Sign < 0),
CreateArray <byte>(value.Abs().ToByteArray())
));
}
public static BigInt Random(this Random generator, BigInt limit)
{
ContractUtils.Requires(limit.Sign > 0, "limit");
ContractUtils.RequiresNotNull(generator, "generator");
BigInt res = BigInt.Zero;
while (true)
{
// if we've run out of significant digits, we can return the total
if (limit == BigInt.Zero)
{
return(res);
}
// if we're small enough to fit in an int, do so
int iLimit;
if (limit.AsInt32(out iLimit))
{
return(res + generator.Next(iLimit));
}
// get the 3 or 4 uppermost bytes that fit into an int
int hiData;
byte[] data = limit.ToByteArray();
int index = data.Length;
while (data[--index] == 0)
{
;
}
if (data[index] < 0x80)
{
hiData = data[index] << 24;
data[index--] = (byte)0;
}
else
{
hiData = 0;
}
hiData |= data[index] << 16;
data[index--] = (byte)0;
hiData |= data[index] << 8;
data[index--] = (byte)0;
hiData |= data[index];
data[index--] = (byte)0;
// get a uniform random number for the uppermost portion of the bigint
byte[] randomData = new byte[index + 2];
generator.NextBytes(randomData);
randomData[index + 1] = (byte)0;
res += new BigInt(randomData);
res += (BigInt)generator.Next(hiData) << ((index + 1) * 8);
// sum it with a uniform random number for the remainder of the bigint
limit = new BigInt(data);
}
}
public static BigInt Random(this Random generator, BigInt limit) {
ContractUtils.Requires(limit.Sign > 0, "limit");
ContractUtils.RequiresNotNull(generator, "generator");
BigInt res = BigInt.Zero;
while (true) {
// if we've run out of significant digits, we can return the total
if (limit == BigInt.Zero) {
return res;
}
// if we're small enough to fit in an int, do so
int iLimit;
if (limit.AsInt32(out iLimit)) {
return res + generator.Next(iLimit);
}
// get the 3 or 4 uppermost bytes that fit into an int
int hiData;
byte[] data = limit.ToByteArray();
int index = data.Length;
while (data[--index] == 0) ;
if (data[index] < 0x80) {
hiData = data[index] << 24;
data[index--] = (byte)0;
} else {
hiData = 0;
}
hiData |= data[index] << 16;
data[index--] = (byte)0;
hiData |= data[index] << 8;
data[index--] = (byte)0;
hiData |= data[index];
data[index--] = (byte)0;
// get a uniform random number for the uppermost portion of the bigint
byte[] randomData = new byte[index + 2];
generator.NextBytes(randomData);
randomData[index + 1] = (byte)0;
res += new BigInt(randomData);
res += (BigInt)generator.Next(hiData) << ((index + 1) * 8);
// sum it with a uniform random number for the remainder of the bigint
limit = new BigInt(data);
}
}