🚀 go-pugleaf

In article <4jbciv$2kk@solutions.solon.com>, vjarnot@mnw.net wrote:

|I have set up an array in the following manner (obviously I just need
|0 or 1) :

|typedef struct my_bits {
|        unsigned the_bit : 1;
|};
|
|my_bits the_array[800][800];
|
|        My question is this : I have read that some operations ( =,+,- are
|what I use) are slower when performed on bits as opposed to other
|types.  My objective is to optimize the code for speed, and I figured
|using less memory would help me do so, now I'm having doubts.  So what
|is more efficient, bits or some other type???

I think the idea of 'bit-fields' have mislead you. The size of the matrix
above is at least 800*800 chars, not 800*800 bits as you might have thought.

This is what the Standard has to say about bit fields:

6.5.2.1. Structure and union specifiers

Constraints

An implementation may allocate any addressable storage unit large enough
to hold a bit-field. If enough space remains, a bit-field that immediately
follows another bit-field in a structure shall be packed into adjacent
bits of the same unit.

[ end of quote ]

The smalles addressable storage unit is a char and an implementation 
is not required to pack adjacent structures in an addressable storage
unit, so you might a well have written:

char the_array[800][800];

because that's the cheapest you can get here without explicit (expensive)
bit fiddling implemented by yourself ...

kind regards,

Jos aka jos@and.nl
-- 
Atnwgqkrl gy zit vgksr, ug qshiqwtzoeqs!