Hello,
I am removing all sprintf() function from my souce code as this function does not allow me to set the proper thread stack size. Does anyone have any function that implements this conversion?
Thanks Andre Moutinho
Too answer your first question, I don't believe it's obvious too you but making such a function is NO TRIVIAL matter. In fact it is quite a bit of work, you must account for +-INF 0 +-NAN just to name a few for floating point. In addition to these you must take care to get correct rounding and the sign of the number as well.
Don't belittle the lowly printf formatting functions because Keil put an inordinate amount of effort to get those to work let alone work correctly (they are very good).
I say this because I've had to do just what you were asking a while ago, it's not exactly a simple exercise AND you MUST know the format of the floating point data you are working with, there is lot of research needed before even starting. If you plan on doing this, good luck, it's about 8 days of work and testing. Also there are a considerable number of academic papers on the subject matter. It's not trivial, and that's just floating point (not the other myriad of functions that the vaprintf family performs).
You may wish to look at the SDCC library if you want a reference. I had to write all of my code in C, and it cannot be made freely available (I don't own it).
I can say it's doable, but you must select carefully what you wish to use out of the vaprintf family of formatting commands first.
Stephen
Hello, I have implemented a ftoa function and made some tests. What do you think? I have spent around 1 hour with tests.. Maybe I have missed something. The str array must be size 20.
void ftoa(float num, char *str) { int intpart = num; int intdecimal; int i; float decimal_part; char decimal[20]; memset(str, 0x0, 20); itoa(num, str, 10); strcat(str, "."); decimal_part = num - intpart; intdecimal = decimal_part * 1000000; if(intdecimal < 0) { intdecimal = -intdecimal; } itoa(intdecimal, decimal, 10); for(i =0;i < (PRECISION - strlen(decimal));i++) { strcat(str, "0"); } strcat(str, decimal); }
itoa(num, str, 10);
And what happens if num is 12345678? You really think a function named IntegerToAscii is up to the task?
Or what do you do if the number is 0.000000000000000012345678?
How do you then store the fractional part in an integer? Or make itoa() make a string of it? Or make the number fit in a 20-character array?
Also remember that sprintf() has more than one way to express a floating point value depending on the formatting string.
Here is the deal - if using sprintf(), you must care about the stack needs. If using own function to convert a floating point value, you must care about the size of the target buffer.
How much do you gain by not getting a stack overflow but instead a buffer overrun?
Hello Westermark, thanks for your reply.
Let me explain what I am doing first. My application is a module that has GPS and GPRS communication. I have a can interface and get some vehicle values such as speed, rotation, hodometer. The ftoa() function will be used only for debug of these values. I have checked their range and will be no larger than 2147483647 and not smaller than 0.00001.
Please read the answers bellow:
>And what happens if num is 12345678? You really think >a function named IntegerToAscii is up to the task?
Yes, it converted with success. Why an itoa() function will not convert this number? The ftoa() function returned 12345678.00000. 12345678 < 2147483647 (0x7ffffff)
>Or what do you do if the number is >0.000000000000000012345678?
This will result in 0.00. But this value is out of the range precision I have stabilished. The result was 0.00000. Thats OK once I have stablished 6 digits of precision.
>How do you then store the fractional part in an >integer?
By multiplying for the precision I want. If I want 0.00001 I then multiply it for 100000.
>Or make itoa() make a string of it? >Or make the number fit in a 20-character array?
Limiting the higher value and precision. I have forgotten to limit the higher value. Will do it.
>Also remember that sprintf() has more than one way to >express a floating point value depending on the >formatting string.
Will not need this.
>Here is the deal - if using sprintf(), you must care >about the stack needs. If using own function to >convert a floating point value, you must care about >the size of the target buffer.
Yes, correct. I will narrow the higher value to 2147483647 (0x7FFFFFFF) or 10 digits. The decimal part in constrained to 5 digits. More one for the '.' and an extra 0x0 for final termination. Total used will be 17 characteres and no buffer overrun.
>How much do you gain by not getting a stack overflow >but instead a buffer overrun?
Nothing, but creating such constraints that works 100% in my application I eliminated both problems.
Regards, Andre
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