Hello,
1.when i use printf with no var_args then the compiler should call puts instead of printf.
ex1:
#include <REGX51.H> #include <stdio.h> void main(void) { printf("This must call puts instead of printf"); }
Program Size: data=30.1 xdata=0 code=1103
ex2:
#include <REGX51.H> #include <stdio.h> void main(void) { puts("This must call puts instead of printf"); }
Program Size: data=9.0 xdata=0 code=168
The above code links the printf function from the library which is huge(produces 1103 bytes).But the compiler can use puts when there is no var_args given which is much smaller than printf(produces 168 bytes).
2.The Compiler must find and remove the duplicate constant strings
ex3:
#include <REGX51.H> #include <stdio.h> void main(void) { puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); }
Program Size: data=9.0 xdata=0 code=334
ex4:
#include <REGX51.H> #include <stdio.h> void main(void) { puts("This string gets duplicated as many time as i use it"); }
Program Size: data=9.0 xdata=0 code=183
3.Bit Test instructions are not used when i actually test for the bit
ex5:
#include <REGX51.H> #include <stdio.h> void main(void) { if(P0^1) { P1 = 10; } } ASSEMBLY LISTING OF GENERATED OBJECT CODE ; FUNCTION main (BEGIN) ; SOURCE LINE # 6 ; SOURCE LINE # 7 ; SOURCE LINE # 8 0000 E580 MOV A,P0 0002 6401 XRL A,#01H 0004 6003 JZ ?C0002 ; SOURCE LINE # 9 ; SOURCE LINE # 10 0006 75900A MOV P1,#0AH ; SOURCE LINE # 11 ; SOURCE LINE # 13 0009 ?C0002: 0009 22 RET ; FUNCTION main (END)
In the above assembly output it should have used a single instruction JNB instead of three MOV,XRL and JZ.This is very basic anybody would object the assembly code produced.
I have not used the compiler much.But the compiler needs a look by the programmers at keil.
The above programs were all compiled with compiler optimisation level set to 9 & favour speed.
About 5 years back i compiled a c51 source code using keil. Now i recompiled the same source code with the latest compiler from keil and compared the two output .hex files. Unfortunately it produced exactly the same output.Here i was expecting some code and data size reduction as the compiler must be capable of optimising more.
It seems there was no improvement on the compiler side.
It is not a complaint but in the interest of improving the compiler.
regards,
S.Sheik mohamed
Hello All,
Thank you all for keeping patience with me.
I agree that all my allegations were complete wrong.
puts Adds extra linefeed to the string so it cannot be used instead of printf.So i was wrong here.
But i think the compiler could be supplied with different versions of printf and let the user decide which printf version is best for him.This way compiler & linker need not struggle to find the best printf.
The optimiser should have used a counter and repeated the following block
MOV R3,#0FFH MOV R2,#HIGH ?SC_0 MOV R1,#LOW ?SC_0 LCALL _puts
No the compiler allocates the string only once.it was again my mistake
I must have used (P0 & 1) instead of (P0 ^ 1) again my mistake.
But when i use (P0 & 1) the compiler understood my intention of bit testing but it has assembled it in a different way.
#include <REGX51.H> #include <stdio.h> void main(void) { if(P0 & 1) { if(P0_1) { P1 = 10; } } } ; FUNCTION main (BEGIN) ; SOURCE LINE # 5 ; SOURCE LINE # 6 ; SOURCE LINE # 7 0000 E580 MOV A,P0 0002 30E006 JNB ACC.0,?C0003 ; SOURCE LINE # 8 ; SOURCE LINE # 9 0005 308103 JNB P0_1,?C0003 ; SOURCE LINE # 10 ; SOURCE LINE # 11 0008 75900A MOV P1,#0AH ; SOURCE LINE # 12 ; SOURCE LINE # 13 ; SOURCE LINE # 15 000B ?C0003: 000B 22 RET ; FUNCTION main (END)
where it could have simply put "JNB P0_1" instead of "mov a,P0" & "jnb ACC.0"
But overall if you compile a source file using an old version of the compiler and again with the new version of the compiler the produced hex file is byte to byte same.
Why the compiler or its optimizer has not improved in reducing the code & data size for many years.
Once again thank for all your patience
That's all very well to say - but what features would go in the "small" printf?
Every user would have their own opinion of what is an "important" feature to have in printf, and what is a "luxury".
In the end, it's probably easiest for the compiler to provide a "full" printf, and, if the user has specific requirements, then they code their own according to those requirements.
The Keil C51 tools have been around for many years - decades, in fact - so, obviously, all the easy optimisations were done years ago.
However, since Keil was acquired by ARM, one might tend to suspect that the non-ARM tools might be receiving less focus...
Simple,
One with full functionality. Another one with floating point support removed.I think this will reduce the code dramatically.
In majority of the application the float may not be neccessary.
Sheik mohamed