Hi, Is there a problem using idata for variables used in "heavy"calculations ? ( heavy = 3 products 2 sums in a same instruction) I use microvision 1.30 dll 1.30 C compiler v5.20 In my program some calculations produce good results when used with data and wrong and changeant results when used with idata. Thanks. Gregory.
I just updated the knowledgebase article to indicate this. Jon
Jon, Can you give any indication of the maximum stack depth the compiler could use when evaluating an arbitrarily complex expression?
I have a hunch such an upper limit can't possibly exist. As far as I can see, "arbritrarily complex" expressions can, almost by definition, require arbitrarily much stack space to evaluate.
"I have a hunch such an upper limit can't possibly exist. As far as I can see, "arbritrarily complex" expressions can, almost by definition, require arbitrarily much stack space to evaluate." Really? It srikes me as a bit strange that the compiler doesn't use the stack for parameter passing or local variables 'due to limitations of the 8051 architecture', however it appears that it arbitrarily and silently pushes whatever quantity of stuff it likes on the stack during evaluation of a complex expression. This is why I would really like a definitive answer from Keil on this subject.
Can you give any indication of the maximum stack depth the compiler could use when evaluating an arbitrarily complex expression? The compiler only stacks temporary results when absolute required. Typically, this is only required in complex expressions using long or float types which include function calls. For example, consider the following:
long a,b,c,d,e; e = (a*b) + (c*d);
long a,b,c,d,e,f,g; e = (a*b) + (c*d) + (f*g);
Really? It srikes me as a bit strange that the compiler doesn't use the stack for parameter passing or local variables 'due to limitations of the 8051 architecture', however it appears that it arbitrarily and silently pushes whatever quantity of stuff it likes on the stack during evaluation of a complex expression. If the compiler used the stack for local variables and function arguments, it would need a way to reference those objects on the stack. It would need a base pointer. R0 or R1 would be required for that. That would leave only 7 registers to be used in the function. Operations with floats or with longs could no longer be performed entirely in registers (like they are now). ALL local variables and function arguments would take longer to access (because indirect accesses are slower on the 8051 then direct accesses). This would slow down ALL programs and would ultimately require more stack space than is used by the current scheme. As it is, you are only penalized (more stack space required) for complex expressions. Jon
Jon, Thank you for your answer.