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alignment                   Definition                  alignment




Alignment refers  to the  fact that some  microprocessors require
the address of a data entity  to be aligned to a numeric boundary
in memory  so that  _a_d_d_r_e_s_s modulo  _n_u_m_b_e_r equals zero.   For ex-
ample,  the M68000  and  the PDP-11  require that  an integer  be
aligned along an even address, i.e., _a_d_d_r_e_s_s%22==00.

Generally  speaking, alignment  is a  problem  only if  you write
programs in assembly  language.  For C programs, COHERENT ensures
that  data  types are  aligned  properly  under foreseeable  con-
ditions.  You  should, however, beware of  copying structures and
of casting a pointer to cchhaarr  to a pointer to a ssttrruucctt, for these
could trigger alignment problems.

Processors react differently to an alignment problem.  On the VAX
or the i8086, it causes a  program to run more slowly, whereas on
the M68000 it causes a bus error.

***** See Also *****

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COHERENT Lexicon                                           Page 1

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