Hi!
The while loop is handled in an inefficient way. Lets have an example:
/*********************************************************************************/
#include <stdlib.h>
#include <msp430x14x.h>
int copy_i(int in);
int main (void) {
unsigned int i;
/**/
i = copy_i(1); /*used to prevent compiler optimisation*/
P1OUT = 0;
while (i<0x8000) {
P1OUT++;
i <<= 1;
}
return CPUOFF;
}
int copy_i(int in) {
return in;
}
/*********************************************************************************/
Objdump outputs the following (fragment):
/*********************************************************************************/
i = copy_i(1); /*used to prevent compiler optimisation*/
1144: 1f 43 mov #1, r15 ;r3 As==01
1146: b0 12 68 11 call #4456 ;#0x1168
P1OUT = 0;
114a: c2 43 21 00 mov.b #0, &0x0021 ;r3 As==00
while (i<0x8000) {
114e: 3f 90 00 80 cmp #-32768,r15 ;#0x8000
1152: 06 2c jc $+14 ;abs 0x1160
P1OUT++;
1154: d2 53 21 00 inc.b &0x0021 ;
i <<= 1;
1158: 0f 5f rla r15 ;
115a: 3f 90 00 80 cmp #-32768,r15 ;#0x8000
115e: fa 2b jnc $-10 ;abs 0x1154
}
/*********************************************************************************/
As can be seen, at address 0x114e the condition is tested as well as at
0x115a. Its not nessecary to test this twice.
Two optimal solutions exist:
1) Test at the end of the loop: When entering the while loop, JMP to the
test.
JMP while_condition
while_body_start: <while_body>
while_condition: <test while_condition>
<conditionally jump to while_body_start>
2) Test at the beginning of the loop: When hitting the end of the loop,
JMP to the test.
while_condition: <test while_condition>
<conditionally jump to while_end>
<while_body>
JMP while_condition:
while_end:
I would suggest to think about the 1st solution, because a do-while loop
would then be equal to a while loop without the initial JMP.
Ralf
