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.TH LIBZAHL 7 libzahl
.SH NAME
libzahl - Big integer library
.SH ETYMOLOGY
The bold uppercase \(aqZ\(aq which represents the
set of all integers is derived from the german word
\(aqzahlen\(aq, whose singular is \(aqzahl\(aq.
.SH DESCRIPTION
.B libzahl
is a C library for arbitrary size integers, that
aims to be usable for rubust programs, and be
fast.
.P
.B libzahl
will accomplish this by using long jumps when an
error is detected, rather than letting the caller
also perform a check. This shall make the code in
the user program cleaner too.
.B libzahl
will use dedicated temporary bignum integers whether
possible, and necessary, for its internal calculations.
.B libzahl
will not deallocate allocations, but rather cache
them for reuse.
.P
With the exception of functions working with strings,
all output parameters are before the input parameters.
.P
Like any self-respecting big number library, libzahl
supports assign values to variables that are also
input variables. However, keep in mind that commutative
functions are optimised for the first operand to also
be the output over the second operand to also be the
input. For example, \fIzadd(a,a,b)\fP should be faster
than \fIzadd(a,b,a)\fP, although both are supported.
Whether or not the function believe that it is more
likely to occur that the input variables are different
that the output variable than the output variable
being the first input variable depends on the function.
Some functions are implemented to believe that the
first is more likely, other fucntions are implemented
to believe that the latter is more likely.
.SH RATIONALE
GMP MP cannot be used for rubust programs. LibTomMath
is too slow, probably because of all memory allocations,
and has an nonintuitive API. Hebimath is promising, but
I think it can be done better.
.SH NOTES
.B libzahl
is currently not thread-safe.
.P
You are strongly discouraged from using
.B libzahl
for cryptographic applications. Instead, use a library
specifically targeting cryptography, otherwise, your
program may be subject to side-channel attacks.
.SH SEE ALSO
.BR zsetup (3)
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