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The slab initialization code includes the calculation of the
slab 'elem_size', which is in turn used to determine the size
(capacity) of the slab. Each element of the slab represents an
array, of length 'stride', of 'elemtype'. (Note that it may be
clearer if the define_commit_slab macro parameter was called
'basetype' rather than 'elemtype'). However, the 'elem_size'
calculation incorrectly uses 'sizeof(struct slabname)' in the
expression, rather than 'sizeof(elemtype)'.
Within the slab access routine, <slabname>_at(), the given commit
'index' is transformed into an (slab#, slot#) pair used to address
the required element (a pointer to the first element of the array
of 'elemtype' associated with that commit). The current code to
calculate these address coordinates multiplies the commit index
by the 'stride' which, at least for the slab#, produces the wrong
result. Using the commit index directly, without scaling by the
'stride', produces the correct 'logical' address.
Also, when allocating a new slab, the size of the allocation only
allows for a slab containing elements of single element arrays of
'elemtype'. This should allow for elements of an array of length
'stride' of 'elemtype'. In order to fix this, we need to change
the element size parameter to xcalloc() by multiplying the current
element size (sizeof(**s->slab)) by the s->stride.
Having changed the calculation of the slot#, we now need to convert
the logical 'nth_slot', by scaling with s->stride, into the correct
physical address.
Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Introduce a header file to define a macro that can define the struct
type, initializer, accessor and cleanup functions to manage a commit
slab. Update the "indegree" topological sort facility using it.
To associate 32 flag bits with each commit, you can write:
define_commit_slab(flag32, uint32);
to declare "struct flag32" type, define an instance of it with
struct flag32 flags;
and initialize it by calling
init_flag32(&flags);
After that, a call to flag32_at() function
uint32 *fp = flag32_at(&flags, commit);
will return a pointer pointing at a uint32 for that commit. Once
you are done with these flags, clean them up with
clear_flag32(&flags);
Callers that cannot hard-code how wide the data to be associated
with the commit be at compile time can use the "_with_stride"
variant to initialize the slab.
Suppose you want to give one bit per existing ref, and paint commits
down to find which refs are descendants of each commit. Saying
typedef uint32 bits320[5];
define_commit_slab(flagbits, bits320);
at compile time will still limit your code with hard-coded limit,
because you may find that you have more than 320 refs at runtime.
The code can declare a commit slab "struct flagbits" like this
instead:
define_commit_slab(flagbits, unsigned char);
struct flagbits flags;
and initialize it by:
nrefs = ... count number of refs ...
init_flagbits_with_stride(&flags, (nrefs + 7) / 8);
so that
unsigned char *fp = flagbits_at(&flags, commit);
will return a pointer pointing at an array of 40 "unsigned char"s
associated with the commit, once you figure out nrefs is 320 at
runtime.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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