HI,Dear all, I did'nt want to use the SRC and ASM,How can Gen the JC instruction in keil?such as following. I used three byte,but used the union struct must define a double word var,You know,The Keil will gen a assemble code more waste the CPU time.So I have following code,to finish a add with 3-byte,but the keil compiler is not smart. CY = 0; V_0 += 0x07; if(CY) { CY = 0; V_1 += 1; if(CY) { CY = 0; V_2 += 1; } } ********************************** ; CY = 0; ; SOURCE LINE # 1254 CLR CY ; V_0 += 0x07; ; SOURCE LINE # 1255 MOV A,#07H ADD A,V_0 MOV V_0,A ; ; if(CY) ; SOURCE LINE # 1257 JNB CY,?C0017 ; { ; SOURCE LINE # 1258 ; CY = 0; ; SOURCE LINE # 1259 CLR CY ; V_1 += 1; ; SOURCE LINE # 1260 INC V_1 ; ; if(CY) ; SOURCE LINE # 1262 JNB CY,?C0017 ; { ; SOURCE LINE # 1263 ; CY = 0; ; SOURCE LINE # 1264 CLR CY ; V += 1; ; SOURCE LINE # 1265 INC V_2 ; }
Hi, I did'nt want to use the SRC and ASM,How can Gen the JC instruction in keil? I do not want to do anything but wish to have billions $$$, gimmy how todo! (= First of all, your example cannot be optimized with JBC (look at the source more careful to know why; HINT: in this case it requires with two additional GOTO). Secondly: when you need with high-optimized code and see that C-compiler cannot give you needed result - why do you not use ASM/ENDASM macro? Okay, now, perhaps you will be surprised about that CY = 0; is not compiled into CLR C. Keil translates it into two-bytes instruction (exactly to "clear bit" instruction with op-code 0xC2 0xbit_number). CLR C is another instruction which takes only one byte of code (it is separate instruction called "clear carry flag" with op-code 0xC3). Do not ask me why does it do such way - I am not the author of the compiler (= It seems that the compiler takes carry flag as a part of the rest bits and not pay attention that there are some assembly commands related to carry flag especially (here I mean the usage CLR C instead of CLR PSW.7). Just ask authors to implement this feature in the future. Anyway, you have a choice: either use LONG variable or make short in-line ASM block - both are useful. As for me so I preffer to write all the program with pure asm; oh well, Erik - kick me then (= cu
The day that a C compiler is "perfect" will never happen. By the old rule 80% of the improvement can be acieved by 20% of the effort and with the market for customers willing to pay 5 times more than currently for a C compiler being minuscule, do not expect the comiler makers to milk every little bit of efficiency. Erik