On 17/02/2014 10:25 PM, Paul Gilmartin wrote:
Then you get to factor in how much "readability" is worth to you.
>
Macros are your friend. But does providing "readability" at the
programming interface level make such a macro unpleasantly
verbose internally?
Unless your desperately need highly optimized code readability is very
important when writing assembler code. I suppose that's definitely the
case for most vendors.
The alternative is to use an optimizing compiler which go out of their
way to remove branches. The following code snippet is a simple routine
to convert a flag byte into a string of binary 1s and 0s. The optimizer
unrolled the loop and used those fancy new load on condition
instructions to remove all branches.
I compiled two versions, one with loop unrolling and one without using
the #pragma nounroll directive. The unrolled version was x3 faster! Now
that's impressive.
* static char buffer[CHAR_BIT + 1];
* int i;
* int numBits = CHAR_BIT;
*
* for ( i = 0; numBits--; i++ )
LR r3,r1
* {
* buffer[i] = ( c & 0x80 ) ? '1' : '0';
LA r0,240
NILF r1,F'128'
LA r8,241
LA r9,241
NILF r3,F'255'
LA r10,241
LTR r1,r1
SLLK r1,r3,1
LOCRE r8,r0
LR r3,r1
NILF r1,F'128'
LA r11,241
NILF r3,F'255'
STC r8,buffer[]0(,r5,9)
LA r2,241
LTR r1,r1
SLL r3,1
LR r1,r3
LOCRE r9,r0
NILF r3,F'128'
STC r9,buffer[]0(,r5,10)
NILF r1,F'255'
LTR r3,r3
SLL r1,1
LOCRE r10,r0
STC r10,buffer[]0(,r5,11)
* c <<= 1;
LR r3,r1
NILF r1,F'128'
NILF r3,F'255'
LTR r1,r1
SLLK r1,r3,1
LR r3,r1
LOCRE r11,r0
NILF r3,F'255'
STC r11,buffer[]0(,r5,12)
LA r8,241
SLLK r9,r3,1
NILF r1,F'128'
LR r10,r9
LA r11,241
LTR r1,r1
LOCRE r8,r0
NILF r10,F'255'
NILF r9,F'128'
STC r8,buffer[]0(,r5,13)
LTR r9,r9
SLLK r8,r10,1
LOCRE r11,r0
LR r9,r8
NILF r8,F'128'
LA r1,241
NILF r9,F'255'
STC r11,buffer[]0(,r5,14)
* }
*
* buffer[i] = '\0';
*
* return buffer;
LA r3,buffer(,r5,9)
LTR r8,r8
SLLK r8,r9,1
LOCRE r1,r0
NILF r8,F'128'
STC r1,buffer[]0(,r5,15)
LTR r8,r8
LOCRE r2,r0
STC r2,buffer[]0(,r5,16)
MVI buffer[]0(r5,17),0
* }
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