[PD] C externals in M1 give errors

Christof Ressi info at christofressi.com
Mon Aug 15 11:46:28 CEST 2022


Edwin has already pointed out the immediate error in your code.

However, there are a lot more problems. First some general issues:

* you need to free the line buffer before returning from the function, 
otherwise there will be a memory leak.

* AFAICT, the string buffer passed to atoi() is not NULL-terminated. 
atoi() stops after encountering a non-numeric character, so depending on 
the data that happens to be on stack, this might appear to work - but it 
can also easily lead to wrong results!

* The default line ending on Windows is CRLF (13 + 10) instead of just 
LF (10), so depending on how the file was created, your code might not 
work correctly.

Now some remarks about the actual code. IIUC, what you try to do is read 
the content of the text file into a two-dimensional array. Your approach 
seems to be the following: loop backwards character by character and 
manually assemble the decimal numbers from individual digits. First off, 
in this case there is need to call atoi() in the first place because you 
already know the value of the digit. On the other hand, this is 
completely unnecessary becauseatoi() can parse /numbers /- not only 
digits! For example, atoi("1024") will output an integer 1024.

Unfortunately, atoi() has a few problems: it does not handle errors and 
it does not give you the position after the number, so you need to 
manually search for whitespace/newlines. 
https://cplusplus.com/reference/cstdlib/strtol/ solves both issues.

The most idiomatic way for reading a sequence of numbers from a textfile 
in C would be https://cplusplus.com/reference/cstdio/sscanf/. Your code 
could be rewritten as follows:

int readbarfile(int a[][8], FILE *f) {
int row = 0;
char * line = NULL;
size_t len = 0;
while (getline(&line, &len, f) != -1) {
int col, value, nread, pos = 0;
for (col = 0; col < 4; col++) {
// We expect 1 converted element.
// (%n does not count, it only tells the current stream position.)
if (sscanf(line + pos, "%d%n", &value, &nread) == 1) {
a[row][col] = value;
pos += nread;
} else {
// handle conversion error
}
}
row++;
     }
free(line);
return row;
}

Since you are dealing with a fixed column size, this could be simplified 
further:

int readbarfile(int a[][8], FILE *f) {
int row = 0, col;
char * line = NULL;
size_t len = 0;
while (getline(&line, &len, f) != -1) {
// We expect 4 integer items. Actually, we can directly read into the 
output array
// because the data type (int) matches the %d specifier.
if (sscanf(line, "%d%d%d%d", &a[row][0], &a[row][1], &a[row][2], 
&a[row][3]) != 4) {
// handle error
}
row++;
     }
free(line);
return row;
}

Christof

On 15.08.2022 08:29, Jaime Oliver wrote:
> Hi Chris, Brad, All,
>
> I managed to trace the error to the function below. It reads a text 
> file and copies its contents to a matrix. The file it's reading is 
> always made of lines with the same number of elements like this below:
>
> 0 4 4 8 32
> 1 4 4 8 32
> 2 4 4 8 32
> ...
>
> The specific error I'm getting right now is that it is reading that 
> number 32 as 29. Again, this same code works fine in all other OSs 
> I've tried.
>
> I'm assuming the issue is in the pow() function and all the 
> typecasting (int), (double) as Chris suggested?
>
> As for compilation, I am using the latest pd_lib_builder as the makefile.
>
> Thanks for your help!
>
> best,
>
> Jaime
>
> code:
>
> int readbarfile(int a[][8], FILE *f)        {
> int i, ii, j, jj, strsize, temp;
> char * line = NULL;
> size_t len = 0;
> ssize_t read;
> char ss[10];
> temp=j=0;
> ii=0;
> while ((read = getline(&line, &len, f)) != -1) {
> jj      = 4;
> strsize = (int) read;
> for (i=strsize-1; i>=0; i--){
> if ( line[i] == (int) 32 || line[i] == (int) 10) { //space or newline
> if(i != (strsize-1)) {
> a[ii][jj] = temp;
> jj--;
>                 }
> j=0;
> temp=0;
>             }
> else     {
> ss[0] = line[i];
> temp += atoi(ss)*( (int) pow((double)10, (double)j) );
> j++;
>             }
>         }
> ii++;
>     }
> return (ii);
> }
>
> On Fri, Aug 12, 2022 at 1:57 PM Chris Clepper <cgclepper at gmail.com> wrote:
>
>     That issue only relates to data corruption in the case of major
>     failures like power loss and kernel panics.  In most of those
>     situations some data loss is not only expected but also the least
>     of your concerns.
>
>     As for the original topic, the first thing to check is the usual
>     problems moving between architectures like endianess, definition
>     of data structures (is long really 32 bits, double 64 bits, etc),
>     memory alignment and compiler settings.  Does the code work with
>     all of the optimizations turned off?
>
>     On Fri, Aug 12, 2022 at 5:58 AM Bastiaan van den Berg
>     <buzz at spacedout.nl> wrote:
>
>         Did you read that M1's storage has so much cache + lies to the
>         OS about cache commitments, leading to data corruption
>         sometimes? https://twitter.com/marcan42/status/1494213855387734019
>
>         On Fri, Aug 12, 2022 at 6:14 AM Jaime Oliver
>         <jaime.oliver2 at gmail.com> wrote:
>
>             Dear all,
>
>             I have a c external that compiles and runs fine on
>             windows, Linux, and Mac Intel systems, but while the exact
>             same code compiles ok on a Mac M1 system, it runs with errors.
>
>             I am trying to figure out the bug, but wonder if anyone
>             has come across something like this? The external itself
>             is not particularly complex. It writes and reads text
>             files, does basic arithmetic, and uses arrays of various
>             sizes.
>
>             Does anyone have any suggestions of where to look first?
>
>             Best,
>
>             Jaime
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>
> -- 
> **********************
> Jaime E Oliver LR
> www.jaimeoliver.pe <http://www.jaimeoliver.pe>
>
>
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