Several directives assemble values for the
current section. For example:
- The .byte and .char
directives place one or more 8-bit values into consecutive bytes of the current section. These
directives are similar to .word, .int, and .long, except that the width of each value is
restricted to 8 bits.
- The
.double directive calculates the double-precision (64-bit) IEEE floating-point
representation of one or more floating-point values and stores them in two consecutive
words in the current section. The .double directive automatically aligns to the
double-word boundary.
- The .field and .bits
directives place a single value into a specified number of bits in the current word. With
.field, you can pack multiple fields into a single word; the assembler does not increment
the SPC until a word is filled. If a field will not fit in the space remaining in the
current word, .field will insert zeros to fill the current word and then place the field
in the next word. The .bits directive is similar but does not force alignment to a field
boundary. See the .field topic and .bits topic.
Figure 6-1 shows how fields are packed into a word. Using the following assembled code, notice
that the SPC does not change
(the fields are packed
into the same
word):
1 00000000 00000003 .field 3,4
2 00000000 00000083 .field 8,5
3 00000000 00002083 .field 16,7
- The
.float directive calculates the single-precision (32-bit) IEEE floating-point
representation of a single floating-point value and stores it in a word in the current
section that is aligned to a word boundary.
- The
.half and .short directives place one or more 16-bit values into
consecutive 16-bit fields (halfwords) in the current section. These directives
automatically align to a short (2-byte) boundary.
- The
.int, .long, and .word directives place one or more 32-bit values
into consecutive 32-bit fields (words) in the current section. These directives
automatically align to a word boundary.
- The .string
and .cstring
directives place 8-bit characters from one or more character strings into the current
section. The .string and .cstring directives are similar to .byte, placing an 8-bit
character in each consecutive byte of the current section. The .cstring directive adds a NUL character needed by
C; the .string directive does not add a NUL character.
- The .ubyte, .uchar, .uhalf,
.uint, .ulong, .ushort, and .uword directives are provided as unsigned versions
of their respective signed directives. These directives are used primarily by the C/C++
compiler to support unsigned types in C/C++.
Note:
Directives that Initialize Constants When Used in a .struct/.endstruct Sequence: The
.bits, .byte, .char, .int, .long, .word, .double, .half,
.short, .string, .ubyte, .uchar, .uhalf, .uint, .ulong, .ushort, .uword, .float, and
.field directives do not
initialize memory when they are part of a .struct/ .endstruct sequence; rather, they define
a member’s size. For more information, see the
.struct/.endstruct directives.
Figure 6-2 compares the .byte, .half, .word, and .string directives using the
following assembled
code:
1 00000000 000000AB .byte 0ABh
2 .align 4
3 00000004 0000CDEF .half 0CDEFh
4 00000008 89ABCDEF .word 089ABCDEFh
5 0000000c 00000068 .string "help"
0000000d 00000065
0000000e 0000006C
0000000f 00000070