Thread: Switch-Case vs If-Else loops

  1. 12-30-2012 #16
    kim15
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    Quote Originally Posted by comocomocomo View Post
    I don't know where is the bottleneck, but...

    But... wait a minute... The 'switch(state)' doesn't make any sense! The variable 'state' will always be zero at this point. It is local, you initialized it to zero, you didn't change it... Maybe you meant to make it 'static':
    in case 0, (the initial state), there is a line that updates the variable 'state'. Same goes for case 1.
  2. 12-30-2012 #17
    comocomocomo
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    Quote Originally Posted by kim15 View Post
    in case 0, (the initial state), there is a line that updates the variable 'state'. Same goes for case 1.
    Yes, but this doesn't help, since 'state' is an automatic local variable, which gets initialized to 0 every time the processor enters the function. If the compiler follows the rules of the language, 'state' will always be 0 when the 'switch' is reached.
  3. 12-30-2012 #18
    kim15
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    oh. so should i declare it as a global?
  4. 12-31-2012 #19
    comocomocomo
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    You don't need it in any other function, and global variables are bad. Leave it local but make it static. It will live like a global variable (whole program execution lifespan, initialized only once), but it will remain private to its function.
  5. 01-28-2013 #20
    Click_here
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    You are using MPLAB from memory -> But you still haven't told us what compiler you are using!

    It would also depend on whether you are using the LITE/Standard/PRO (You pay more money, your code gets optimised more)

    The best way would be to actually see what is being generated -> The switch statement is usually better when programming your PIC, because it generates an optimised branching table.

    Do the two different ways in your code. Click "View" -> "Disassembly listing"

    I'm using the C18 compiler PRO -

    Code:
    280:               	if (test_data == 1)
 039AE    0102     MOVLB 0x2
 039B0    0E01     MOVLW 0x1
 039B2    19FE     XORWF 0xfe, W, BANKED
 039B4    E101     BNZ 0x39b8
 039B6    51FF     MOVF 0xff, W, BANKED
 039B8    E10C     BNZ 0x39d2
281:               	{
282:               		puts("1");
 039BA    0E76     MOVLW 0x76
 039BC    6EE6     MOVWF 0xfe6, ACCESS
 039BE    0E4E     MOVLW 0x4e
 039C0    6EE6     MOVWF 0xfe6, ACCESS
 039C2    0E00     MOVLW 0
 039C4    6EE6     MOVWF 0xfe6, ACCESS
 039C6    ECFA     CALL 0x53f4, 0
 039C8    F029     NOP
 039CA    52E5     MOVF 0xfe5, F, ACCESS
 039CC    52E5     MOVF 0xfe5, F, ACCESS
 039CE    52E5     MOVF 0xfe5, F, ACCESS
283:               	}
284:               	else if	(test_data == 2)
 039D0    D04F     BRA 0x3a70
 039D2    0E02     MOVLW 0x2
 039D4    19FE     XORWF 0xfe, W, BANKED
 039D6    E101     BNZ 0x39da
 039D8    51FF     MOVF 0xff, W, BANKED
 039DA    E10C     BNZ 0x39f4
285:               	{
286:               		puts("2");
 039DC    0E74     MOVLW 0x74
 039DE    6EE6     MOVWF 0xfe6, ACCESS
 039E0    0E4E     MOVLW 0x4e
 039E2    6EE6     MOVWF 0xfe6, ACCESS
 039E4    0E00     MOVLW 0
 039E6    6EE6     MOVWF 0xfe6, ACCESS
 039E8    ECFA     CALL 0x53f4, 0
 039EA    F029     NOP
 039EC    52E5     MOVF 0xfe5, F, ACCESS
 039EE    52E5     MOVF 0xfe5, F, ACCESS
 039F0    52E5     MOVF 0xfe5, F, ACCESS
287:               	}
288:               	else if	(test_data == 3)
 039F2    D03E     BRA 0x3a70
 039F4    0E03     MOVLW 0x3
 039F6    19FE     XORWF 0xfe, W, BANKED
 039F8    E101     BNZ 0x39fc
 039FA    51FF     MOVF 0xff, W, BANKED
 039FC    E10C     BNZ 0x3a16
289:               	{
290:               		puts("3");
 039FE    0E72     MOVLW 0x72
 03A00    6EE6     MOVWF 0xfe6, ACCESS
 03A02    0E4E     MOVLW 0x4e
 03A04    6EE6     MOVWF 0xfe6, ACCESS
 03A06    0E00     MOVLW 0
 03A08    6EE6     MOVWF 0xfe6, ACCESS
 03A0A    ECFA     CALL 0x53f4, 0
 03A0C    F029     NOP
 03A0E    52E5     MOVF 0xfe5, F, ACCESS
 03A10    52E5     MOVF 0xfe5, F, ACCESS
 03A12    52E5     MOVF 0xfe5, F, ACCESS
291:               	}	
292:               	else if	(test_data == 4)
 03A14    D02D     BRA 0x3a70
 03A16    0E04     MOVLW 0x4
 03A18    19FE     XORWF 0xfe, W, BANKED
 03A1A    E101     BNZ 0x3a1e
 03A1C    51FF     MOVF 0xff, W, BANKED
 03A1E    E10C     BNZ 0x3a38
293:               	{
294:               		puts("4");
 03A20    0E70     MOVLW 0x70
 03A22    6EE6     MOVWF 0xfe6, ACCESS
 03A24    0E4E     MOVLW 0x4e
 03A26    6EE6     MOVWF 0xfe6, ACCESS
 03A28    0E00     MOVLW 0
 03A2A    6EE6     MOVWF 0xfe6, ACCESS
 03A2C    ECFA     CALL 0x53f4, 0
 03A2E    F029     NOP
 03A30    52E5     MOVF 0xfe5, F, ACCESS
 03A32    52E5     MOVF 0xfe5, F, ACCESS
 03A34    52E5     MOVF 0xfe5, F, ACCESS
295:               	}
296:               	else if	(test_data == 5)
 03A36    D01C     BRA 0x3a70
 03A38    0E05     MOVLW 0x5
 03A3A    19FE     XORWF 0xfe, W, BANKED
 03A3C    E101     BNZ 0x3a40
 03A3E    51FF     MOVF 0xff, W, BANKED
 03A40    E10C     BNZ 0x3a5a
297:               	{
298:               		puts("5");
 03A42    0E6E     MOVLW 0x6e
 03A44    6EE6     MOVWF 0xfe6, ACCESS
 03A46    0E4E     MOVLW 0x4e
 03A48    6EE6     MOVWF 0xfe6, ACCESS
 03A4A    0E00     MOVLW 0
 03A4C    6EE6     MOVWF 0xfe6, ACCESS
 03A4E    ECFA     CALL 0x53f4, 0
 03A50    F029     NOP
 03A52    52E5     MOVF 0xfe5, F, ACCESS
 03A54    52E5     MOVF 0xfe5, F, ACCESS
 03A56    52E5     MOVF 0xfe5, F, ACCESS
299:               	}
300:               	else 
 03A58    D00B     BRA 0x3a70
301:               	{
302:               		puts("?");
 03A5A    0E6C     MOVLW 0x6c
 03A5C    6EE6     MOVWF 0xfe6, ACCESS
 03A5E    0E4E     MOVLW 0x4e
 03A60    6EE6     MOVWF 0xfe6, ACCESS
 03A62    0E00     MOVLW 0
 03A64    6EE6     MOVWF 0xfe6, ACCESS
 03A66    ECFA     CALL 0x53f4, 0
 03A68    F029     NOP
 03A6A    52E5     MOVF 0xfe5, F, ACCESS
 03A6C    52E5     MOVF 0xfe5, F, ACCESS
 03A6E    52E5     MOVF 0xfe5, F, ACCESS
303:               	}
304:               	
305:               	switch (test_data)
 03A70    0E05     MOVLW 0x5
 03A72    0102     MOVLB 0x2
 03A74    19FE     XORWF 0xfe, W, BANKED
 03A76    E101     BNZ 0x3a7a
 03A78    51FF     MOVF 0xff, W, BANKED
 03A7A    E045     BZ 0x3b06
 03A7C    0E04     MOVLW 0x4
 03A7E    19FE     XORWF 0xfe, W, BANKED
 03A80    E101     BNZ 0x3a84
 03A82    51FF     MOVF 0xff, W, BANKED
 03A84    E034     BZ 0x3aee
 03A86    0E03     MOVLW 0x3
 03A88    19FE     XORWF 0xfe, W, BANKED
 03A8A    E101     BNZ 0x3a8e
 03A8C    51FF     MOVF 0xff, W, BANKED
 03A8E    E023     BZ 0x3ad6
 03A90    0E02     MOVLW 0x2
 03A92    19FE     XORWF 0xfe, W, BANKED
 03A94    E101     BNZ 0x3a98
 03A96    51FF     MOVF 0xff, W, BANKED
 03A98    E012     BZ 0x3abe
 03A9A    0E01     MOVLW 0x1
 03A9C    19FE     XORWF 0xfe, W, BANKED
 03A9E    E101     BNZ 0x3aa2
 03AA0    51FF     MOVF 0xff, W, BANKED
 03AA2    E001     BZ 0x3aa6
 03AA4    D03C     BRA 0x3b1e
306:               	{ 
307:               		case 1:
308:               			puts("1");
 03AA6    0E76     MOVLW 0x76
 03AA8    6EE6     MOVWF 0xfe6, ACCESS
 03AAA    0E4E     MOVLW 0x4e
 03AAC    6EE6     MOVWF 0xfe6, ACCESS
 03AAE    0E00     MOVLW 0
 03AB0    6EE6     MOVWF 0xfe6, ACCESS
 03AB2    ECFA     CALL 0x53f4, 0
 03AB4    F029     NOP
 03AB6    52E5     MOVF 0xfe5, F, ACCESS
 03AB8    52E5     MOVF 0xfe5, F, ACCESS
 03ABA    52E5     MOVF 0xfe5, F, ACCESS
309:               			break;
 03ABC    D03B     BRA 0x3b34
310:               			
311:               		case 2:
312:               			puts("2");
 03ABE    0E74     MOVLW 0x74
 03AC0    6EE6     MOVWF 0xfe6, ACCESS
 03AC2    0E4E     MOVLW 0x4e
 03AC4    6EE6     MOVWF 0xfe6, ACCESS
 03AC6    0E00     MOVLW 0
 03AC8    6EE6     MOVWF 0xfe6, ACCESS
 03ACA    ECFA     CALL 0x53f4, 0
 03ACC    F029     NOP
 03ACE    52E5     MOVF 0xfe5, F, ACCESS
 03AD0    52E5     MOVF 0xfe5, F, ACCESS
 03AD2    52E5     MOVF 0xfe5, F, ACCESS
313:               			break;
 03AD4    D02F     BRA 0x3b34
314:               			
315:               		case 3:
316:               			puts("3");
 03AD6    0E72     MOVLW 0x72
 03AD8    6EE6     MOVWF 0xfe6, ACCESS
 03ADA    0E4E     MOVLW 0x4e
 03ADC    6EE6     MOVWF 0xfe6, ACCESS
 03ADE    0E00     MOVLW 0
 03AE0    6EE6     MOVWF 0xfe6, ACCESS
 03AE2    ECFA     CALL 0x53f4, 0
 03AE4    F029     NOP
 03AE6    52E5     MOVF 0xfe5, F, ACCESS
 03AE8    52E5     MOVF 0xfe5, F, ACCESS
 03AEA    52E5     MOVF 0xfe5, F, ACCESS
317:               			break;
 03AEC    D023     BRA 0x3b34
318:               			
319:               		case 4:
320:               			puts("4");
 03AEE    0E70     MOVLW 0x70
 03AF0    6EE6     MOVWF 0xfe6, ACCESS
 03AF2    0E4E     MOVLW 0x4e
 03AF4    6EE6     MOVWF 0xfe6, ACCESS
 03AF6    0E00     MOVLW 0
 03AF8    6EE6     MOVWF 0xfe6, ACCESS
 03AFA    ECFA     CALL 0x53f4, 0
 03AFC    F029     NOP
 03AFE    52E5     MOVF 0xfe5, F, ACCESS
 03B00    52E5     MOVF 0xfe5, F, ACCESS
 03B02    52E5     MOVF 0xfe5, F, ACCESS
321:               			break;
 03B04    D017     BRA 0x3b34
322:               			
323:               		case 5:
324:               			puts("5");
 03B06    0E6E     MOVLW 0x6e
 03B08    6EE6     MOVWF 0xfe6, ACCESS
 03B0A    0E4E     MOVLW 0x4e
 03B0C    6EE6     MOVWF 0xfe6, ACCESS
 03B0E    0E00     MOVLW 0
 03B10    6EE6     MOVWF 0xfe6, ACCESS
 03B12    ECFA     CALL 0x53f4, 0
 03B14    F029     NOP
 03B16    52E5     MOVF 0xfe5, F, ACCESS
 03B18    52E5     MOVF 0xfe5, F, ACCESS
 03B1A    52E5     MOVF 0xfe5, F, ACCESS
325:               			break;
 03B1C    D00B     BRA 0x3b34
326:               			
327:               		default:
328:               			puts("?");
 03B1E    0E6C     MOVLW 0x6c
 03B20    6EE6     MOVWF 0xfe6, ACCESS
 03B22    0E4E     MOVLW 0x4e
 03B24    6EE6     MOVWF 0xfe6, ACCESS
 03B26    0E00     MOVLW 0
 03B28    6EE6     MOVWF 0xfe6, ACCESS
 03B2A    ECFA     CALL 0x53f4, 0
 03B2C    F029     NOP
 03B2E    52E5     MOVF 0xfe5, F, ACCESS
 03B30    52E5     MOVF 0xfe5, F, ACCESS
 03B32    52E5     MOVF 0xfe5, F, ACCESS
329:               	}
    Fact - Beethoven wrote his first symphony in C
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