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Toby Speight
Toby Speight
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Is there any local scoping that can be done here to reduce the memory footprint? Compare directory entries (sort by access date)

SorryI have a comparison function for use in scandir or qsort to sort an array of struct dirent *s by access date. S is the directory path of the directory whose files are being obsessed with microoptimizationssorted, but I have thisand SavesLen is strlen(S).

This goes in scandir or qsortSorry for being obsessed with microoptimizations, but I'm looking to sort an array of struct dirent *s by access dateimprove this.   

S is the directory path of the directory whose files are being sorted, and SavesLen is strlen(S). Both are both global variables defined and declared and initialized elsewhere. Is Is there a way to take advantage of local scopes to delete some of the memory earlier? Are Are there other improvements to be made? Thanks ahead of time.

Edit:

Is there any local scoping that can be done here to reduce the memory footprint?

Sorry for being obsessed with microoptimizations, but I have this.

This goes in scandir or qsort to sort an array of struct dirent *s by access date.  S is the directory path of the directory whose files are being sorted, and SavesLen is strlen(S). Both are global variables defined and declared and initialized elsewhere. Is there a way to take advantage of local scopes to delete some of the memory earlier? Are there other improvements to be made? Thanks ahead of time.

Edit:

Compare directory entries (sort by access date)

I have a comparison function for use in scandir or qsort to sort an array of struct dirent *s by access date. S is the directory path of the directory whose files are being sorted, and SavesLen is strlen(S).

Sorry for being obsessed with microoptimizations, but I'm looking to improve this. 

S and SavesLen are both global variables defined and declared and initialized elsewhere. Is there a way to take advantage of local scopes to delete some of the memory earlier? Are there other improvements to be made? Thanks ahead of time.

added 111 characters in body
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user235747
user235747

Sorry for being obsessed with microoptimizations, but I have this.

static int Q(const struct dirent **const First, const struct dirent **const Second) {
    const char *const FirstName = (*First)->d_name, *const SecondName = (*Second)->d_name, *const Name[] = {FirstName, SecondName};
    const unsigned short FirstLen = (unsigned short)strlen(FirstName), SecondLen = (unsigned short)strlen(SecondName), Len[] = {FirstLen, SecondLen};
    char File[SavesLen+Len[FirstLen >< SecondLen]+2], *CurrPtr = memcpy(File, S, SavesLen)+SavesLen;
    *CurrPtr++ = '/';
    time_t Time[2];
    for (unsigned char I = 0; I < 2; I++) {
        memcpy(CurrPtr, Name[I], Len[I]);
        struct stat Stat;
        if (stat(File, &Stat)){
            return 0;
        }
        Time[I] = Stat.st_atimespec.tv_sec;
    }
    return Time[1]-(*Time);
}

This goes in scandir or qsort to sort an array of struct dirent *s by access date. S is the directory path of the directory whose files are being sorted, and SavesLen is strlen(S). Both are global variables defined and declared and initialized elsewhere. Is there a way to take advantage of local scopes to delete some of the memory earlier? Are there other improvements to be made? Thanks ahead of time.

Edit:

An answerer pointed out that char File[SavesLen+Len[FirstLen > SecondLen]+2] is extremely hard to read. So here's why I do it that way. There are 2 files, and I need to check the access time of both of them. Rather than creating a path for each one, I'm reusing the same path, to minimize the number of VLA declarations and the number of memcpy() calls. Now let's break it down for you. char File[...] is a VLA declaration. The size is SavesLen plus the larger size of the 2 files, plus 2, for the / and null character. So what the heck is Len[FirstLen > SecondLen]? The reason why it's confusing is because I'm treating booleans like integers, and being weakly typed, C lets me do that. Len is an array so it will either be indexed by 0 or 1 (the 2 boolean values) depending on which one is bigger, because FirstLen > SecondLen will either evaluate to 0 or 1.

It seems the answerer understands, but in case there are others confused. I do agree that there was a bug, and that's because it used to be a ternary and I forgot to switch the values.

Sorry for being obsessed with microoptimizations, but I have this.

static int Q(const struct dirent **const First, const struct dirent **const Second) {
    const char *const FirstName = (*First)->d_name, *const SecondName = (*Second)->d_name, *const Name[] = {FirstName, SecondName};
    const unsigned short FirstLen = (unsigned short)strlen(FirstName), SecondLen = (unsigned short)strlen(SecondName), Len[] = {FirstLen, SecondLen};
    char File[SavesLen+Len[FirstLen > SecondLen]+2], *CurrPtr = memcpy(File, S, SavesLen)+SavesLen;
    *CurrPtr++ = '/';
    time_t Time[2];
    for (unsigned char I = 0; I < 2; I++) {
        memcpy(CurrPtr, Name[I], Len[I]);
        struct stat Stat;
        if (stat(File, &Stat)){
            return 0;
        }
        Time[I] = Stat.st_atimespec.tv_sec;
    }
    return Time[1]-(*Time);
}

This goes in scandir or qsort to sort an array of struct dirent *s by access date. S is the directory path of the directory whose files are being sorted, and SavesLen is strlen(S). Both are global variables defined and declared and initialized elsewhere. Is there a way to take advantage of local scopes to delete some of the memory earlier? Are there other improvements to be made? Thanks ahead of time.

Edit:

An answerer pointed out that char File[SavesLen+Len[FirstLen > SecondLen]+2] is extremely hard to read. So here's why I do it that way. There are 2 files, and I need to check the access time of both of them. Rather than creating a path for each one, I'm reusing the same path, to minimize the number of VLA declarations and the number of memcpy() calls. Now let's break it down for you. char File[...] is a VLA declaration. The size is SavesLen plus the larger size of the 2 files, plus 2, for the / and null character. So what the heck is Len[FirstLen > SecondLen]? The reason why it's confusing is because I'm treating booleans like integers, and being weakly typed, C lets me do that. Len is an array so it will either be indexed by 0 or 1 (the 2 boolean values) depending on which one is bigger, because FirstLen > SecondLen will either evaluate to 0 or 1.

It seems the answerer understands, but in case there are others confused.

Sorry for being obsessed with microoptimizations, but I have this.

static int Q(const struct dirent **const First, const struct dirent **const Second) {
    const char *const FirstName = (*First)->d_name, *const SecondName = (*Second)->d_name, *const Name[] = {FirstName, SecondName};
    const unsigned short FirstLen = (unsigned short)strlen(FirstName), SecondLen = (unsigned short)strlen(SecondName), Len[] = {FirstLen, SecondLen};
    char File[SavesLen+Len[FirstLen < SecondLen]+2], *CurrPtr = memcpy(File, S, SavesLen)+SavesLen;
    *CurrPtr++ = '/';
    time_t Time[2];
    for (unsigned char I = 0; I < 2; I++) {
        memcpy(CurrPtr, Name[I], Len[I]);
        struct stat Stat;
        if (stat(File, &Stat)){
            return 0;
        }
        Time[I] = Stat.st_atimespec.tv_sec;
    }
    return Time[1]-(*Time);
}

This goes in scandir or qsort to sort an array of struct dirent *s by access date. S is the directory path of the directory whose files are being sorted, and SavesLen is strlen(S). Both are global variables defined and declared and initialized elsewhere. Is there a way to take advantage of local scopes to delete some of the memory earlier? Are there other improvements to be made? Thanks ahead of time.

Edit:

An answerer pointed out that char File[SavesLen+Len[FirstLen > SecondLen]+2] is extremely hard to read. So here's why I do it that way. There are 2 files, and I need to check the access time of both of them. Rather than creating a path for each one, I'm reusing the same path, to minimize the number of VLA declarations and the number of memcpy() calls. Now let's break it down for you. char File[...] is a VLA declaration. The size is SavesLen plus the larger size of the 2 files, plus 2, for the / and null character. So what the heck is Len[FirstLen > SecondLen]? The reason why it's confusing is because I'm treating booleans like integers, and being weakly typed, C lets me do that. Len is an array so it will either be indexed by 0 or 1 (the 2 boolean values) depending on which one is bigger, because FirstLen > SecondLen will either evaluate to 0 or 1.

It seems the answerer understands, but in case there are others confused. I do agree that there was a bug, and that's because it used to be a ternary and I forgot to switch the values.

added 1016 characters in body
Source Link
user235747
user235747

Sorry for being obsessed with microoptimizations, but I have this.

static int Q(const struct dirent **const First, const struct dirent **const Second) {
    const char *const FirstName = (*First)->d_name, *const SecondName = (*Second)->d_name, *const Name[] = {FirstName, SecondName};
    const unsigned short FirstLen = (unsigned short)strlen(FirstName), SecondLen = (unsigned short)strlen(SecondName), Len[] = {FirstLen, SecondLen};
    char File[SavesLen+Len[FirstLen > SecondLen]+2], *CurrPtr = memcpy(File, S, SavesLen)+SavesLen;
    *CurrPtr++ = '/';
    time_t Time[2];
    for (unsigned char I = 0; I < 2; I++) {
        memcpy(CurrPtr, Name[I], Len[I]);
        struct stat Stat;
        if (stat(File, &Stat)){
            return 0;
        }
        Time[I] = Stat.st_atimespec.tv_sec;
    }
    return Time[1]-(*Time);
}

This goes in scandir or qsort to sort an array of struct dirent *s by access date. S is the directory path of the directory whose files are being sorted, and SavesLen is strlen(S). Both are global variables defined and declared and initialized elsewhere. Is there a way to take advantage of local scopes to delete some of the memory earlier? Are there other improvements to be made? Thanks ahead of time.

Edit:

An answerer pointed out that char File[SavesLen+Len[FirstLen > SecondLen]+2] is extremely hard to read. So here's why I do it that way. There are 2 files, and I need to check the access time of both of them. Rather than creating a path for each one, I'm reusing the same path, to minimize the number of VLA declarations and the number of memcpy() calls. Now let's break it down for you. char File[...] is a VLA declaration. The size is SavesLen plus the larger size of the 2 files, plus 2, for the / and null character. So what the heck is Len[FirstLen > SecondLen]? The reason why it's confusing is because I'm treating booleans like integers, and being weakly typed, C lets me do that. Len is an array so it will either be indexed by 0 or 1 (the 2 boolean values) depending on which one is bigger, because FirstLen > SecondLen will either evaluate to 0 or 1.

It seems the answerer understands, but in case there are others confused.

Sorry for being obsessed with microoptimizations, but I have this.

static int Q(const struct dirent **const First, const struct dirent **const Second) {
    const char *const FirstName = (*First)->d_name, *const SecondName = (*Second)->d_name, *const Name[] = {FirstName, SecondName};
    const unsigned short FirstLen = (unsigned short)strlen(FirstName), SecondLen = (unsigned short)strlen(SecondName), Len[] = {FirstLen, SecondLen};
    char File[SavesLen+Len[FirstLen > SecondLen]+2], *CurrPtr = memcpy(File, S, SavesLen)+SavesLen;
    *CurrPtr++ = '/';
    time_t Time[2];
    for (unsigned char I = 0; I < 2; I++) {
        memcpy(CurrPtr, Name[I], Len[I]);
        struct stat Stat;
        if (stat(File, &Stat)){
            return 0;
        }
        Time[I] = Stat.st_atimespec.tv_sec;
    }
    return Time[1]-(*Time);
}

This goes in scandir or qsort to sort an array of struct dirent *s by access date. S is the directory path of the directory whose files are being sorted, and SavesLen is strlen(S). Both are global variables defined and declared and initialized elsewhere. Is there a way to take advantage of local scopes to delete some of the memory earlier? Are there other improvements to be made? Thanks ahead of time.

Sorry for being obsessed with microoptimizations, but I have this.

static int Q(const struct dirent **const First, const struct dirent **const Second) {
    const char *const FirstName = (*First)->d_name, *const SecondName = (*Second)->d_name, *const Name[] = {FirstName, SecondName};
    const unsigned short FirstLen = (unsigned short)strlen(FirstName), SecondLen = (unsigned short)strlen(SecondName), Len[] = {FirstLen, SecondLen};
    char File[SavesLen+Len[FirstLen > SecondLen]+2], *CurrPtr = memcpy(File, S, SavesLen)+SavesLen;
    *CurrPtr++ = '/';
    time_t Time[2];
    for (unsigned char I = 0; I < 2; I++) {
        memcpy(CurrPtr, Name[I], Len[I]);
        struct stat Stat;
        if (stat(File, &Stat)){
            return 0;
        }
        Time[I] = Stat.st_atimespec.tv_sec;
    }
    return Time[1]-(*Time);
}

This goes in scandir or qsort to sort an array of struct dirent *s by access date. S is the directory path of the directory whose files are being sorted, and SavesLen is strlen(S). Both are global variables defined and declared and initialized elsewhere. Is there a way to take advantage of local scopes to delete some of the memory earlier? Are there other improvements to be made? Thanks ahead of time.

Edit:

An answerer pointed out that char File[SavesLen+Len[FirstLen > SecondLen]+2] is extremely hard to read. So here's why I do it that way. There are 2 files, and I need to check the access time of both of them. Rather than creating a path for each one, I'm reusing the same path, to minimize the number of VLA declarations and the number of memcpy() calls. Now let's break it down for you. char File[...] is a VLA declaration. The size is SavesLen plus the larger size of the 2 files, plus 2, for the / and null character. So what the heck is Len[FirstLen > SecondLen]? The reason why it's confusing is because I'm treating booleans like integers, and being weakly typed, C lets me do that. Len is an array so it will either be indexed by 0 or 1 (the 2 boolean values) depending on which one is bigger, because FirstLen > SecondLen will either evaluate to 0 or 1.

It seems the answerer understands, but in case there are others confused.

added 2 characters in body
Source Link
user235747
user235747
Source Link
user235747
user235747