CommandLineToArgvA implementation ported from WINE CommandLineToArgvW in a reduced and easier to read format

CommandLineToArgvA.c

LPSTR* WINAPI CommandLineToArgvA(LPSTR lpCmdline, int* numargs) {
    DWORD argc;
    LPSTR* argv;
    LPSTR s;
    LPSTR d;
    LPSTR cmdline;
    int qcount, bcount;
    if (!numargs || !*lpCmdline) {
        SetLastError(ERROR_INVALID_PARAMETER);
        return NULL;
    }
    argc = 1;
    s = lpCmdline;
    if (*s == '"') {
        ++s;
        while (*s) {
            if (*s++ == '"') break;
        }
    } else {
        while (*s && *s != ' ' && *s != '\t') ++s;
    }
    while (*s == ' ' || *s == '\t') ++s;
    if (*s) ++argc;
    qcount = 0;
    bcount = 0;
    while (*s) {
        if ((*s == ' ' || *s == '\t') && !qcount) {
            while (*s == ' ' || *s == '\t') ++s;
            if (*s) ++argc;
            bcount = 0;
        } else if (*s == '\\') {
            ++bcount;
            ++s;
        } else if (*s == '"') {
            if (!(bcount & 1)) ++qcount;
            ++s;
            bcount = 0;
            while (*s == '"') {
                ++qcount;
                ++s;
            }
            qcount = qcount % 3;
            if (qcount == 2) qcount = 0;
        } else {
            bcount = 0;
            ++s;
        }
    }
    argv = LocalAlloc(LMEM_FIXED, (argc + 1) * sizeof(LPSTR) + (strlen(lpCmdline) + 1) * sizeof(char));
    if (!argv) return NULL;
    cmdline = (LPSTR)(argv + argc + 1);
    strcpy(cmdline, lpCmdline);
    argv[0] = d = cmdline;
    argc = 1;
    if (*d == '"') {
        s = d + 1;
        while (*s) {
            if (*s == '"') {
                ++s;
                break;
            }
            *d++ = *s++;
        }
    } else {
        while (*d && *d != ' ' && *d != '\t') ++d;
        s = d;
        if (*s) ++s;
    }
    *d++ = 0;
    while (*s == ' ' || *s == '\t') ++s;
    if (!*s) {
        argv[argc] = NULL;
        *numargs = argc;
        return argv;
    }
    argv[argc++] = d;
    qcount = 0;
    bcount = 0;
    while (*s) {
        if ((*s == ' ' || *s == '\t') && !qcount) {
            *d++ = 0;
            bcount = 0;
            do {
                ++s;
            } while (*s == ' ' || *s == '\t');
            if (*s) argv[argc++] = d;
        } else if (*s=='\\') {
            *d++ = *s++;
            ++bcount;
        } else if (*s == '"') {
            if (!(bcount & 1)) {
                d -= bcount / 2;
                ++qcount;
            } else {
                d = d - bcount / 2 - 1;
                *d++ = '"';
            }
            ++s;
            bcount = 0;
            while (*s == '"') {
                if (++qcount == 3) {
                    *d++ = '"';
                    qcount = 0;
                }
                ++s;
            }
            if (qcount == 2) qcount = 0;
        } else {
            *d++ = *s++;
            bcount = 0;
        }
    }
    *d = '\0';
    argv[argc] = NULL;
    *numargs = argc;
    return argv;
}