math.mp.Integer: Return two's complement length

This commit is contained in:
Eugen Wissner 2017-05-08 21:09:52 +02:00
parent 708d95db49
commit 06620dc5df

View File

@ -178,12 +178,64 @@ struct Integer
allocator.resize(this.rep, 0);
}
static private const short[16] bitCounts = [
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
];
// Counts the number of LSBs before the first non-zero bit.
private ptrdiff_t countLSBs() const pure nothrow @safe @nogc
{
if (this.size == 0)
{
return 0;
}
ptrdiff_t bits;
for (bits = 0; (bits < this.size) && (this.rep[bits] == 0); ++bits)
{
}
digit nonZero = this.rep[bits];
bits *= digitBitCount;
/* now scan this digit until a 1 is found */
if ((nonZero & 0x01) == 0)
{
digit bitCountsPos;
do
{
bitCountsPos = nonZero & 0x0f;
bits += bitCounts[bitCountsPos];
nonZero >>= 4;
}
while (bitCountsPos == 0);
}
return bits;
}
/**
* Returns: Integer byte length.
* Returns: Number of bytes in the two's complement representation.
*/
@property size_t length() const pure nothrow @safe @nogc
{
return (countBits() + 7) / 8; // Round up.
if (this.sign)
{
const bitCount = countBits();
auto length = bitCount + (8 - (bitCount & 0x07));
if (((countLSBs() + 1) == bitCount) && ((bitCount & 0x07) == 0))
{
--length;
}
return length / 8;
}
else if (this.size == 0)
{
return 0;
}
else
{
return (countBits() / 8) + 1;
}
}
/**