diff options
Diffstat (limited to 'gcc/doc/tm.texi')
| -rw-r--r-- | gcc/doc/tm.texi | 24 |
1 files changed, 13 insertions, 11 deletions
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi index 496a4a2..8436e89 100644 --- a/gcc/doc/tm.texi +++ b/gcc/doc/tm.texi @@ -1181,17 +1181,19 @@ go slower in that case, define this macro as 0. Define this if you wish to imitate the way many other C compilers handle alignment of bit-fields and the structures that contain them. -The behavior is that the type written for a bit-field (@code{int}, -@code{short}, or other integer type) imposes an alignment for the -entire structure, as if the structure really did contain an ordinary -field of that type. In addition, the bit-field is placed within the -structure so that it would fit within such a field, not crossing a -boundary for it. - -Thus, on most machines, a bit-field whose type is written as @code{int} -would not cross a four-byte boundary, and would force four-byte -alignment for the whole structure. (The alignment used may not be four -bytes; it is controlled by the other alignment parameters.) +The behavior is that the type written for a named bit-field (@code{int}, +@code{short}, or other integer type) imposes an alignment for the entire +structure, as if the structure really did contain an ordinary field of +that type. In addition, the bit-field is placed within the structure so +that it would fit within such a field, not crossing a boundary for it. + +Thus, on most machines, a named bit-field whose type is written as +@code{int} would not cross a four-byte boundary, and would force +four-byte alignment for the whole structure. (The alignment used may +not be four bytes; it is controlled by the other alignment parameters.) + +An unnamed bit-field will not affect the alignment of the containing +structure. If the macro is defined, its definition should be a C expression; a nonzero value for the expression enables this behavior. |