The Renesas M32R version of as
has a few architecture
specific directives:
low expression
The low
directive computes the value of its expression and
places the lower 16-bits of the result into the immediate-field of the
instruction. For example:
or3 r0, r0, #low(0x12345678) ; compute r0 = r0 | 0x5678 add3, r0, r0, #low(fred) ; compute r0 = r0 + low 16-bits of address of fred
high expression
¶The high
directive computes the value of its expression and
places the upper 16-bits of the result into the immediate-field of the
instruction. For example:
seth r0, #high(0x12345678) ; compute r0 = 0x12340000 seth, r0, #high(fred) ; compute r0 = upper 16-bits of address of fred
shigh expression
¶The shigh
directive is very similar to the high
directive. It also computes the value of its expression and places
the upper 16-bits of the result into the immediate-field of the
instruction. The difference is that shigh
also checks to see
if the lower 16-bits could be interpreted as a signed number, and if
so it assumes that a borrow will occur from the upper-16 bits. To
compensate for this the shigh
directive pre-biases the upper
16 bit value by adding one to it. For example:
For example:
seth r0, #shigh(0x12345678) ; compute r0 = 0x12340000 seth r0, #shigh(0x00008000) ; compute r0 = 0x00010000
In the second example the lower 16-bits are 0x8000. If these are treated as a signed value and sign extended to 32-bits then the value becomes 0xffff8000. If this value is then added to 0x00010000 then the result is 0x00008000.
This behaviour is to allow for the different semantics of the
or3
and add3
instructions. The or3
instruction
treats its 16-bit immediate argument as unsigned whereas the
add3
treats its 16-bit immediate as a signed value. So for
example:
seth r0, #shigh(0x00008000) add3 r0, r0, #low(0x00008000)
Produces the correct result in r0, whereas:
seth r0, #shigh(0x00008000) or3 r0, r0, #low(0x00008000)
Stores 0xffff8000 into r0.
Note - the shigh
directive does not know where in the assembly
source code the lower 16-bits of the value are going set, so it cannot
check to make sure that an or3
instruction is being used rather
than an add3
instruction. It is up to the programmer to make
sure that correct directives are used.
.m32r
The directive performs a similar thing as the -m32r command line option. It tells the assembler to only accept M32R instructions from now on. An instructions from later M32R architectures are refused.
.m32rx
The directive performs a similar thing as the -m32rx command line option. It tells the assembler to start accepting the extra instructions in the M32RX ISA as well as the ordinary M32R ISA.
.m32r2
The directive performs a similar thing as the -m32r2 command line option. It tells the assembler to start accepting the extra instructions in the M32R2 ISA as well as the ordinary M32R ISA.
.little
The directive performs a similar thing as the -little command line option. It tells the assembler to start producing little-endian code and data. This option should be used with care as producing mixed-endian binary files is fraught with danger.
.big
The directive performs a similar thing as the -big command line option. It tells the assembler to start producing big-endian code and data. This option should be used with care as producing mixed-endian binary files is fraught with danger.