[PD] C externals in M1 give errors
Brad Garton
garton at columbia.edu
Mon Aug 15 16:41:47 CEST 2022
Christof points out problems with atoi() and line endings -- I ran into
similar problems some time ago and resorted to sscanf()-ing what I read
from the file to format it it 'properly' in memory before doing the
conversion.
brad
On Mon, Aug 15, 2022 at 3:39 AM Christof Ressi <info at christofressi.com>
wrote:
> 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 because atoi() 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/
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__cplusplus.com_reference_cstdlib_strtol_&d=DwMFaQ&c=009klHSCxuh5AI1vNQzSO0KGjl4nbi2Q0M1QLJX9BeE&r=TUSlFmJ_9hRhpnUmWLtwdEo8SXGhxgz2NDS43-6hnKg&m=5HPO3yP5cO7EAoTCLdg8pt_pFjHj1F_sb9fmPj7RONcdAsUqm3_qp-YU6QFsBjhO&s=aojlAfmm0qrla86hNuWi_ywdPlUiiQh4BXpvgdwQljA&e=>
> 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/
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__cplusplus.com_reference_cstdio_sscanf_&d=DwMFaQ&c=009klHSCxuh5AI1vNQzSO0KGjl4nbi2Q0M1QLJX9BeE&r=TUSlFmJ_9hRhpnUmWLtwdEo8SXGhxgz2NDS43-6hnKg&m=5HPO3yP5cO7EAoTCLdg8pt_pFjHj1F_sb9fmPj7RONcdAsUqm3_qp-YU6QFsBjhO&s=NQmHaCycNfkE6pc2Lw_VRoGaSYkZeYhDtqKZr8ih0jM&e=>.
> 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
>>> <https://urldefense.proofpoint.com/v2/url?u=https-3A__twitter.com_marcan42_status_1494213855387734019&d=DwMFaQ&c=009klHSCxuh5AI1vNQzSO0KGjl4nbi2Q0M1QLJX9BeE&r=TUSlFmJ_9hRhpnUmWLtwdEo8SXGhxgz2NDS43-6hnKg&m=5HPO3yP5cO7EAoTCLdg8pt_pFjHj1F_sb9fmPj7RONcdAsUqm3_qp-YU6QFsBjhO&s=oiKhcMBiqQPZXOuU59byzkz6mJov0w-_kEaq00lsSXg&e=>
>>>
>>> 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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>>>>
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>>>
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>>
>
>
> --
> **********************
> Jaime E Oliver LR
> www.jaimeoliver.pe
> <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.jaimeoliver.pe&d=DwMFaQ&c=009klHSCxuh5AI1vNQzSO0KGjl4nbi2Q0M1QLJX9BeE&r=TUSlFmJ_9hRhpnUmWLtwdEo8SXGhxgz2NDS43-6hnKg&m=5HPO3yP5cO7EAoTCLdg8pt_pFjHj1F_sb9fmPj7RONcdAsUqm3_qp-YU6QFsBjhO&s=816FeXVgLvL2QY607BjMTQHSAVONVbxVVVkeYicfCok&e=>
>
>
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