Monday, 20 September 2010

BSDNT - v0.11 generic test code

It's time we improved our test framework for all the functions we are
adding, before things get out-of-control.

The best strategy is to actually write an interpreter for a small
expression parser which allows us to test arbitrary expressions.
However, that would be a distraction at this point, so we opt to
simply add some convenience functions.

In particular, we'll add some new random functions which generate
lists of random words and random garbage collected nn's. Our only aim
here is to simplify our test code and cut down the number of lines of

We don't want to make it *more* complicated for people to use, and
C89 places some hard limits on us in that regard.

The first step is to add two new files, test.c and test.h which
will contain our garbage collection and random functions.

We begin by adding an enum type_t, which parameterises all the different
types our garbage collection can clean up. At the moment we only need
one type, NN.

Next we add a variadic function (variable number of arguments) which
creates a whole bunch of random words. Unfortunately C89 doesn't support
variadic macros, so we need to pass pointers to the words, so that the
actual words can be modified.

This random function takes a flag which specifies what type of random
number we want. Specifically we'll have flags for ODD, NONZERO, ANY.

C is also so stupid that we actually need to tell it explicitly, or mark
somehow, the number of arguments we are giving to the variadic function.
In C99 one can work around this by wrapping a variadic function with a
variadic macro. But we don't have that facility here. We choose to simply
pass NULL as the final argument to variadic functions.

We also introduce a global garbage stack which will keep a pointer to all
the objects allocated so far, so that a garbage collector can clean them
up later on, when called. The fact that this garbage is global makes it not
threadsafe, but we are only using the test support for test code at this
point and so we don't care about thread safety. Later we could pass a
context around as a parameter if we wanted to make it threadsafe.

We also add a gc _cleanup function, which cleans away all the garbage, so
that memory leaks don't occur. Later we could expand this function to do
redzone checking and various other automatic tests on the garbage it is
disposing of.

Now we can add some convenience functions for generating random
multiprecision integers.

The randoms_of_len function again takes a NULL terminated list of
*pointers* to nn_t's and both initialises them to the given length and
sets them to random limbs. We can specify various flags here, such as
ANY, FULL, the latter returning a multiprecision integer with exactly
the given number of limbs, with the top limb being nonzero (unless
the number of limbs requested is zero).

Now that we have all this, in our test file test.h, we define a macro
TEST_START which takes a number of iterations and simply sets up a loop
with that many iterations. A TEST_END function then calls garbage collection
to clean up at the end.

Finally, we add a test_generics function, which generates some random values
using our new generics and then cleans up.

By running a program called valgrind over our test code, we can see if all
the memory used by our generics actually got cleaned up after use.

We now roll out these changes to the rest of our test code. We note that the
entire test file is now about two-thirds of the length it was before we rewrote

The new branch is on github: v0.11

Previous article: v0.10 - mod1_preinv
Next article: v0.12 - mul_classical

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