Truncate utility for Windows

truncate.c

// cl /nologo truncate.c kernel32.lib shell32.lib /O1 /GS- /Gs9999999 /GF /kernel /link /ENTRY:main /NODEFAULTLIB /SUBSYSTEM:windows /NOCOFFGRPINFO /ALIGN:16 /MERGE:.rdata=.text /MERGE:.pdata=.text /OUT:truncate.exe

#define WIN32_LEAN_AND_MEAN
#include <Windows.h>
#include <shellapi.h>
#include <stdio.h>

BOOL ParseUInt64W(const wchar_t* s, const wchar_t** end, ULONGLONG* out) {
    ULONGLONG v = 0;
    const wchar_t* p = s;
    if (*p < L'0' || *p > L'9') {
        if (end) *end = s;
        return FALSE;
    }
    while (*p >= L'0' && *p <= L'9') {
        ULONGLONG d = (ULONGLONG)(*p - L'0');
        if (v > (MAXULONGLONG - d) / 10) return FALSE;
        v = v * 10 + d;
        ++p;
    }
    if (end) *end = p;
    *out = v;
    return TRUE;
}

BOOL ParseSizeW(const wchar_t* s, int* ps, LONGLONG* out) {
    int sign = 0;
    if (*s == L'+') { sign = +1; ++s; }
    else if (*s == L'-') { sign = -1; ++s; }

    const wchar_t* end;
    ULONGLONG n;
    if (!ParseUInt64W(s, &end, &n)) return FALSE;

    ULONGLONG mult = 1;
    switch (*end) {
        case L'K': case L'k': mult = 1ULL << 10; break;
        case L'M': case L'm': mult = 1ULL << 20; break;
        case L'G': case L'g': mult = 1ULL << 30; break;
        case L'T': case L't': mult = 1ULL << 40; break;
        case L'\0': break;
        default: return FALSE;
    }

    LONGLONG delta = (LONGLONG)(n * mult);
    *out = (sign == 0) ? delta : sign * delta;
	*ps = sign;
    return TRUE;
}

int main() {
	int argc = 0;
	wchar_t** argv = CommandLineToArgvW(GetCommandLineW(), &argc);
	
	int mode = 0;
	wchar_t* wszSize = NULL;
	wchar_t* wszFileName = NULL;
	for (int i = 1; i < argc; ++i) {
		if (mode == 0 && (
			(argv[i][0] == L'-' && argv[i][1] == L's') ||
			(argv[i][0] == L'-' && argv[i][1] == L'-' && argv[i][2] == L's' && argv[i][3] == L'i' && argv[i][4] == L'z' && argv[i][5] == L'e'))) {
			mode = 1;
		} else if (mode == 1) {
			wszSize = argv[i];
			mode = 0;
		} else if (mode == 0) {
			wszFileName = argv[i];
		}
	}
	
	if (!wszSize || !wszFileName)
		goto end1;
	
	HANDLE hFile = CreateFileW(wszFileName, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
	if (!hFile || hFile == INVALID_HANDLE_VALUE)
		goto end1;
	
	LARGE_INTEGER li;
	int sign = 0;
	if (!ParseSizeW(wszSize, &sign, &li.QuadPart))
		goto end2;
	
	if (!SetFilePointerEx(hFile, li, 0, sign ? FILE_END : FILE_BEGIN))
		goto end2;
	
	if (!SetEndOfFile(hFile))
		goto end2;

end2:
	CloseHandle(hFile);
	argc = GetLastError();
	goto end;
end1:
	argc = GetLastError();
end:
	LocalFree(argv);
	return argc;
}