mpz_t variables can be converted to and from arbitrary words of binary
data with the following functions.
Set rop from an array of word data at op.
The parameters specify the format of the data. count many words are read, each size bytes. order can be 1 for most significant word first or -1 for least significant first. Within each word endian can be 1 for most significant byte first, -1 for least significant first, or 0 for the native endianness of the host CPU. The most significant nails bits of each word are skipped, this can be 0 to use the full words.
There is no sign taken from the data, rop will simply be a positive
integer. An application can handle any sign itself, and apply it for instance
There are no data alignment restrictions on op, any address is allowed.
Here’s an example converting an array of
unsigned long data, most
significant element first, and host byte order within each value.
unsigned long a; /* Initialize z and a */ mpz_import (z, 20, 1, sizeof(a), 0, 0, a);
This example assumes the full
sizeof bytes are used for data in the
given type, which is usually true, and certainly true for
everywhere we know of. However on Cray vector systems it may be noted that
int are always stored in 8 bytes (and with
sizeof indicating that) but use only 32 or 46 bits. The nails
feature can account for this, by passing for instance
Fill rop with word data from op.
The parameters specify the format of the data produced. Each word will be size bytes and order can be 1 for most significant word first or -1 for least significant first. Within each word endian can be 1 for most significant byte first, -1 for least significant first, or 0 for the native endianness of the host CPU. The most significant nails bits of each word are unused and set to zero, this can be 0 to produce full words.
The number of words produced is written to
countp can be
NULL to discard the count. rop must have
enough space for the data, or if rop is
NULL then a result array
of the necessary size is allocated using the current GMP allocation function
(see Custom Allocation). In either case the return value is the
destination used, either rop or the allocated block.
If op is non-zero then the most significant word produced will be
non-zero. If op is zero then the count returned will be zero and
nothing written to rop. If rop is
NULL in this case, no
block is allocated, just
NULL is returned.
The sign of op is ignored, just the absolute value is exported. An
application can use
mpz_sgn to get the sign and handle it as desired.
(see Integer Comparisons)
There are no data alignment restrictions on rop, any address is allowed.
When an application is allocating space itself the required size can be
determined with a calculation like the following. Since
always returns at least 1,
count here will be at least one, which
avoids any portability problems with
malloc(0), though if
zero no space at all is actually needed (or written).
numb = 8*size - nail; count = (mpz_sizeinbase (z, 2) + numb-1) / numb; p = malloc (count * size);