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math.mp.Integer.toVector return two's complement

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Eugen Wissner 2017-05-09 06:27:30 +02:00
parent 06620dc5df
commit 1cb9349226
1 changed files with 43 additions and 50 deletions
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93
source/tanya/math/mp.d
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@ -1389,77 +1389,70 @@ struct Integer
return result;
}
// Returns 2^^n.
private Integer exp2(size_t n) const nothrow @safe @nogc
{
auto ret = Integer(allocator);
const bytes = n / digitBitCount;
ret.grow(bytes + 1);
ret.size = bytes + 1;
ret.rep[bytes] = (cast(digit) 1) << (n % digitBitCount);
return ret;
}
/**
* Returns: Two's complement representation of the integer.
*/
Vector!ubyte toVector() const nothrow @safe @nogc
out (vector)
{
assert(vector.length == length);
}
body
{
Vector!ubyte vector;
bool firstBit;
ubyte carry;
if (this.size == 0)
{
return vector;
}
vector.reserve(this.size * digit.sizeof);
const bitCount = countBits();
const remainingBits = bitCount & 0x07;
// The first digit needs extra handling since it can have leading
// non significant zeros.
int digitCount = digitBitCount - 8;
const first = this.rep[this.size - 1];
const prevBitCount = ((this.size - 1) * digitBitCount);
const fullBytesBitCount = ((prevBitCount - 1) / 8 + 1) * 8;
// Find out the right alignment of the first byte.
if ((fullBytesBitCount - prevBitCount) == 0)
vector.reserve(bitCount / 8);
if (remainingBits == 0)
{
digitCount -= digit.sizeof * 8 - digitBitCount;
vector.insertBack(ubyte.init);
}
for (; digitCount >= 0; digitCount -= 8)
Integer tmp;
if (this.sign)
{
if (firstBit || ((first >> digitCount) != 0))
auto length = bitCount + (8 - remainingBits);
if (((countLSBs() + 1) == bitCount) && (remainingBits == 0))
{
firstBit = true;
vector.insertBack(cast(ubyte) (first >> digitCount));
length -= 8;
}
}
if (digitCount >= -8)
{
carry = (first << -digitCount) & 0xff;
digitCount += digitBitCount;
tmp = exp2(length) + this;
}
else
{
carry = 0;
digitCount = digitBitCount - 8;
tmp = this;
}
foreach_reverse (d; this.rep[0 .. this.size - 1])
do
{
if (carry != 0) // Check the carry from the previous digit.
{
vector.insertBack(cast(ubyte) (carry | (d >> digitCount)));
digitCount -= 8;
}
// Write the digit by bytes.
for (; digitCount >= 0; digitCount -= 8)
{
vector.insertBack(cast(ubyte) (d >> digitCount));
}
// Check for an incomplete byte.
if (digitCount >= -8)
{
carry = (d << -digitCount) & 0xff;
digitCount += digitBitCount;
}
else
{
carry = 0;
digitCount = digitBitCount - 8;
}
}
if (carry != 0)
{
vector.insertBack(cast(ubyte) (carry >> (digitBitCount - digitCount)));
vector.insertBack(cast(ubyte) (tmp.rep[0] & 0xff));
tmp >>= 8;
}
while (tmp != 0);
vector[].reverse();
return vector;
}