Hi,
I want to reduce code size of my DSP code. The Infineon processor I'm
using sup****ts two different types of instructions, a 16 and a 32 bit
version. There are no equivalent 16bit instructions for all 32bit
instruction and the 16bit instructions are obviously more constrained
in terms of their operands. So, for example for jumps, the maximal
displacement can be 8bit large while the 32bit jumps sup****t up to
16bit. For my question, I however assume that the size of the displacement
operand is not an issue.
What I want to do in particular is the substitution of 32bit jumps
by equivalent 16bit jumps. This is a piece of assembly code I often
find in my program and I would like to optimize:
move d1, 10
move d2, 1000
jge d2, d1, target
So, the constants 10 and 1000 are stored into registers d1 and d2
and finally the jump (jump greater/equal) is taken to "target" if
the value of register d2 >= d1.
To reduce code size, I'd like to replace this 32bit jump by a
16bit jump which is defined as:
jz/jnz dX, target
So, whenever the value of register dX is zero (jz) or is not
zero (jnz), the branch is taken.
Now I'm wondering how the first code can be efficiently transformed
into an semantically equal code where jz/jnz is used. Obviously,
jz/jnz has a slightly different meaning compared to jge but I hope
that there is a way to transform the second code without using too
many additional instructions (which would undo the code size
reduction I achieve with the jump instruction replacement).
A possible solution (but not applicable due to an additional code size
increase) could look like:
move d1, 10
move d2, 1000
sub d3, d2, d1
ge d4, d2, 0 # d4 becomes 1 if d2 >= 0
jnz d4, target
Do you see any better solution. It's fully OK if you give an
example in any pseudo assembler code.
Thank you.
Tim
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