Related
I want to read a bin-file with a size under 2mb.
At the moment my code for reading the bin file looks like this:
edit:
#define MAX_BYTES_IN_FILE 500000 // ~ 2mb
#define ERROR_FILE 1
int get_byte_from_file(FILE *stream, unsigned char *dataarray) {
int counter = 0;
while ((dataarray[counter] = fgetc(stream)) != EOF) {
counter += 1;
}
return counter;
}
Main looks like this for the example use of the function.
int main(int argc, char **argv) {
FILE *datei;
unsigned int number_of_bytes;
unsigned char *dataarray;
dataarray = (unsigned char *)malloc(sizeof(unsigned char) * MAX_BYTES_IN_FILE);
datei = fopen(argv[1], "rb");
number_of_bytes = get_byte_from_file(datei, dataarray);
for (int i = 0; i < number_of_bytes; i++)
printf("%x ", dataarray[i]);
return 0;
}
Maybe I did a simple mistake but cant see it the error is still: Segmentation fault (core dumped)
This line is sufficient to crash your program:
while ((dataarray[counter] = fgetc(stream)) != EOF) {
Let's go through it step by step:
fgetc(stream) reads a byte and returns its value or EOF. Because a byte can have any possible value, fgetc() returns a larger int, which can hold an EOF value that is distinct from any byte value that might be found in the file.
You assign this int value to an unsigned char. An EOF value will be truncated to this datatype.
The value of the assignment is of type unsigned char, and the converted EOF value is not equal to EOF anymore. Thus, the comparison always fails, and your program keeps fetching data until the buffer overruns and nasty things begin to happen.
You need to store the result of fgetc() in an int variable until you've checked that it is indeed not the EOF value.
Maybe something like this.
void *readfile(FILE *fi, long *filesize)
{
void *buff;
fseek(fi, 0, SEEK_END);
*filesize = ftell(fi);
fseek(fi, 0, SEEK_SET);
buff = malloc(*filesize);
if(buff)
{
fread(buff, 1, *filesize, fi);
}
return buff;
}
You need to add error checks- I did not as it is only the idea.
And your usage:
int main(int argc, char **argv) {
FILE *datei;
long number_of_bytes;
unsigned char *dataarray;
datei=fopen(argv[1],"rb");
dataarray = readfile(datei, &number_of_bytes);
for (int i=0;dataarray && i<number_of_bytes;i++)
printf("%hhx ",dataarray[i]);
return 0;
}
The reason you get a segmentation fault is your allocation is incorrect: you allocate MAX_BYTES_IN_FILE bytes instead of unsigned int elements. As allocated, the array has only MAX_BYTES_IN_FILE / sizeof(unsigned int) elements, whereas the file is probably MAX_BYTES_IN_FILE * sizeof(unsigned int) bytes long.
You are reading bytes from the file (values between 0 and 255) but you use unsigned int elements. What is the logic? Does the file contain 32-bit values or individual bytes?
Once you can confirm that the file contents is exactly the same as the representation of the array in memory, you can use fread() to read the whole file in a single call.
I have wrote a c code which takes the input value of key and message makes call to openssl hmac functions and generate result of mac code.
Input values are collected from NIST Test Vectors
#define KEY_SIZE 11 // in bytes
#define MSG_SIZE 129 // in bytes
#include <stdio.h>
#include <string.h>
#include <openssl/hmac.h>
void str2hex(char *, char*, int);
int main() {
char *key, *msg;
unsigned char keyy[KEY_SIZE], msgt[MSG_SIZE], temp[4];
unsigned char* result;
unsigned int i, len = 20,Tlen = 10;
key = "";//values specified below
msg ="";//values specified below
/*CONVERT STRING TO HEX DIGITS - KEY*/
str2hex(key, keyy, KEY_SIZE);
//CONVERT STRING TO HEX DIGITS - MSG*//
str2hex(msg, msgt, MSG_SIZE);
result = (unsigned char*)malloc(sizeof(char) * len);
HMAC_CTX ctx;
HMAC_CTX_init(&ctx);
HMAC_Init_ex(&ctx, keyy, strlen(keyy), EVP_sha1(), NULL);
HMAC_Update(&ctx, (unsigned char*)&msgt, strlen(msgt));
HMAC_Final(&ctx, result, &len);
HMAC_CTX_cleanup(&ctx);
printf("HMAC digest: ");
for (i = 0; i < Tlen; i++)
printf("%02x", result[i]);
printf("\n");
free(result);
return 0;
}
//===================== string to hex conversion
================================//
void str2hex(char *str, char *hex, int len) {
int tt, ss;
unsigned char temp[4];
for (tt = 0, ss = 0; tt < len, ss < 2 * len; tt++, ss += 2) {
temp[0] = '0';
temp[1] = 'x';
temp[2] = str[ss];
temp[3] = str[ss + 1];
hex[tt] = (int) strtol(temp, NULL, 0);
}
}
//---------------------------------------------------------------------------------//
The first input given:
Key = 82f3b69a1bff4de15c33
Msg = fcd6d98bef45ed6850806e96f255fa0c8114b72873abe8f43c10bea7c1df706f10458e6d4e1c9201f057b8492fa10fe4b541d0fc9d41ef839acff1bc76e3fdfebf2235b5bd0347a9a6303e83152f9f8db941b1b94a8a1ce5c273b55dc94d99a171377969234134e7dad1ab4c8e46d18df4dc016764cf95a11ac4b491a2646be1
Output generated:
HMAC digest: 1ba0e66cf72efc349207
Nist_Mac = 1ba0e66cf72efc349207
It matches so success
But for the Second input
Key = 4766e6fe5dffc98a5c50
Msg = d68b828a153f5198c005ee36c0af2ff92e84907517f01d9b7c7993469df5c21078fa356a8c9715ece2414be94e10e547f32cbb8d0582523ed3bb0066046e51722094aa44533d2c876e82db402fbb00a6c2f2cc3487973dfc1674463e81e42a39d9402941f39b5e126bafe864ea1648c0a5be0a912697a87e4f8eabf79cbf130e
Output generated:
HMAC digest: ca96f112a79882074b63
Nist_Mac = 007e4504041a12f9e345
Its failing.If any one could check my code and kindly let me know what am i doing wrong it will be really helpfull.
You have two issues here.
The first is that you're using strlen on an array of characters that may contain a null byte. Since this function counts the number of bytes until it find a null byte, you won't get what you expect if your array contains a null byte (as is the case for your second example).
Instead of using strlen on the byte array to determine the length, use the actual length of the data. Since you're converting a string containing hex digits to bytes, the length of the byte array is half the length of the input string.
HMAC_Init_ex(&ctx, keyy, strlen(key)/2, EVP_sha1(), NULL);
HMAC_Update(&ctx, msgt, strlen(msg)/2);
Note also that you should pass msgt to HMAC_Update, not &msgt, as the latter is a pointer to an array.
The second issue is in your str2hex function. When you construct temp, you don't have enough space for a terminating null byte. This causes strtol, which expects a null-terminated string, to read past the end of the array. This invokes undefined behavior.
In this particular case you're "lucky" that it works, as the byte in memory that follows temp happens to contain either a null byte or a non-digit. You can't however depend on this behavior. Fix this by making temp one byte longer and explicitly setting that byte to 0. And while you're at it, you should also fix the signed / unsigned mismatch in your function arguments and change the type of temp to an unsigned char array.
void str2hex(char *, unsigned char*, int);
...
void str2hex(char *str, unsigned char *hex, int len) {
int tt, ss;
char temp[5];
for (tt = 0, ss = 0; tt < len, ss < 2 * len; tt++, ss += 2) {
temp[0] = '0';
temp[1] = 'x';
temp[2] = str[ss];
temp[3] = str[ss + 1];
temp[4] = 0;
hex[tt] = strtol(temp, NULL, 0);
}
}
At byte position 58 in the message, you have a 0x00 byte (null). Since you're doing an strlen(msgt), this results in 58 instead of 128. Excerpt from the documentation (emphasis mine):
The C library function size_t strlen(const char *str) computes the length of the string str up to, but not including the terminating null character.
Just use the proper length of the message and don't use string operations on char arrays that do not contain printable bytes.
I'm trying to convert a float to char string I used sprintf, as the following
float temperature = getTemperature();
char array[15];
sprintf(array, "temperature %f", temperature);
int length = strlen(array);
protocol_WriteMessage(length,(unsigned char*)&array);
but protocol_WriteMessage accepts unsigned char *, so I casted it, but the program crashes.
void protocol_WriteMessage( UINT16 wLen, UINT8 *pbData )
{
UINT16 crc_calc;
// Calculate transmitt CRC16
crc_calc = calc_crc16(&pbData[COMM_POS_COMMAND1], wLen-COMM_POS_COMMAND1);
comm_states.TxActive = true; // signal that the Tx_UART is working
// write data without further checks
hal_uart_WriteBuffer( wLen, pbData );
}
First of all use a safer alternative like snprintf(), and then remove the & address of operator from the call.
To use snprintf() you need to do something like this
int result;
char array[32]; // This should be big enough
result = snprintf(array, sizeof(array), "temperature %f", temperature);
if ((result == -1) || (result >= sizeof(array))) {
// It means that array is too small, or some other error
// occurred such that `snprintf' has returned -1
}
protocol_WriteMessage(length, (unsigned char *) array);
since array is already a pointer to the first element of itself, which is of type char then it's type is char * when passed like that as a pointer, using the & operator is clearly wrong and casting only hides the fact that you made a mistake.
I am using the itoa() function to convert an int into string, but it is giving an error:
undefined reference to `itoa'
collect2: ld returned 1 exit status
What is the reason? Is there some other way to perform this conversion?
Use snprintf, it is more portable than itoa.
itoa is not part of standard C, nor is it part of standard C++; but, a lot of compilers and associated libraries support it.
Example of sprintf
char* buffer = ... allocate a buffer ...
int value = 4564;
sprintf(buffer, "%d", value);
Example of snprintf
char buffer[10];
int value = 234452;
snprintf(buffer, 10, "%d", value);
Both functions are similar to fprintf, but output is written into an array rather than to a stream. The difference between sprintf and snprintf is that snprintf guarantees no buffer overrun by writing up to a maximum number of characters that can be stored in the buffer.
Use snprintf - it is standard an available in every compilator. Query it for the size needed by calling it with NULL, 0 parameters. Allocate one character more for null at the end.
int length = snprintf( NULL, 0, "%d", x );
char* str = malloc( length + 1 );
snprintf( str, length + 1, "%d", x );
...
free(str);
Before I continue, I must warn you that itoa is NOT an ANSI function — it's not a standard C function. You should use sprintf to convert an int into a string.
itoa takes three arguments.
The first one is the integer to be converted.
The second is a pointer to an array of characters - this is where the string is going to be stored. The program may crash if you pass in a char * variable, so you should pass in a normal sized char array and it will work fine.
The last one is NOT the size of the array, but it's the BASE of your number - base 10 is the one you're most likely to use.
The function returns a pointer to its second argument — where it has stored the converted string.
itoa is a very useful function, which is supported by some compilers - it's a shame it isn't support by all, unlike atoi.
If you still want to use itoa, here is how should you use it. Otherwise, you have another option using sprintf (as long as you want base 8, 10 or 16 output):
char str[5];
printf("15 in binary is %s\n", itoa(15, str, 2));
Better use sprintf(),
char stringNum[20];
int num=100;
sprintf(stringNum,"%d",num);
Usually snprintf() is the way to go:
char str[16]; // could be less but i'm too lazy to look for the actual the max length of an integer
snprintf(str, sizeof(str), "%d", your_integer);
You can make your own itoa, with this function:
void my_utoa(int dataIn, char* bffr, int radix){
int temp_dataIn;
temp_dataIn = dataIn;
int stringLen=1;
while ((int)temp_dataIn/radix != 0){
temp_dataIn = (int)temp_dataIn/radix;
stringLen++;
}
//printf("stringLen = %d\n", stringLen);
temp_dataIn = dataIn;
do{
*(bffr+stringLen-1) = (temp_dataIn%radix)+'0';
temp_dataIn = (int) temp_dataIn / radix;
}while(stringLen--);}
and this is example:
char buffer[33];
int main(){
my_utoa(54321, buffer, 10);
printf(buffer);
printf("\n");
my_utoa(13579, buffer, 10);
printf(buffer);
printf("\n");
}
void itos(int value, char* str, size_t size) {
snprintf(str, size, "%d", value);
}
..works with call by reference. Use it like this e.g.:
int someIntToParse;
char resultingString[length(someIntToParse)];
itos(someIntToParse, resultingString, length(someIntToParse));
now resultingString will hold your C-'string'.
char string[something];
sprintf(string, "%d", 42);
Similar implementation to Ahmad Sirojuddin but slightly different semantics. From a security perspective, any time a function writes into a string buffer, the function should really "know" the size of the buffer and refuse to write past the end of it. I would guess its a part of the reason you can't find itoa anymore.
Also, the following implementation avoids performing the module/devide operation twice.
char *u32todec( uint32_t value,
char *buf,
int size)
{
if(size > 1){
int i=size-1, offset, bytes;
buf[i--]='\0';
do{
buf[i--]=(value % 10)+'0';
value = value/10;
}while((value > 0) && (i>=0));
offset=i+1;
if(offset > 0){
bytes=size-i-1;
for(i=0;i<bytes;i++)
buf[i]=buf[i+offset];
}
return buf;
}else
return NULL;
}
The following code both tests the above code and demonstrates its correctness:
int main(void)
{
uint64_t acc;
uint32_t inc;
char buf[16];
size_t bufsize;
for(acc=0, inc=7; acc<0x100000000; acc+=inc){
printf("%u: ", (uint32_t)acc);
for(bufsize=17; bufsize>0; bufsize/=2){
if(NULL != u32todec((uint32_t)acc, buf, bufsize))
printf("%s ", buf);
}
printf("\n");
if(acc/inc > 9)
inc*=7;
}
return 0;
}
Like Edwin suggested, use snprintf:
#include <stdio.h>
int main(int argc, const char *argv[])
{
int n = 1234;
char buf[10];
snprintf(buf, 10, "%d", n);
printf("%s\n", buf);
return 0;
}
If you really want to use itoa, you need to include the standard library header.
#include <stdlib.h>
I also believe that if you're on Windows (using MSVC), then itoa is actually _itoa.
See http://msdn.microsoft.com/en-us/library/yakksftt(v=VS.100).aspx
Then again, since you're getting a message from collect2, you're likely running GCC on *nix.
see this example
#include <stdlib.h> // for itoa() call
#include <stdio.h>
int main() {
int num = 145;
char buf[5];
// convert 123 to string [buf]
itoa(num, buf, 10);
// print our string
printf("%s\n", buf);
return 0;
}
see this link having other examples.
itoa() function is not defined in ANSI-C, so not implemented by default for some platforms (Reference Link).
s(n)printf() functions are easiest replacement of itoa(). However itoa (integer to ascii) function can be used as a better overall solution of integer to ascii conversion problem.
itoa() is also better than s(n)printf() as performance depending on the implementation. A reduced itoa (support only 10 radix) implementation as an example: Reference Link
Another complete itoa() implementation is below (Reference Link):
#include <stdbool.h>
#include <string.h>
// A utility function to reverse a string
char *reverse(char *str)
{
char *p1, *p2;
if (! str || ! *str)
return str;
for (p1 = str, p2 = str + strlen(str) - 1; p2 > p1; ++p1, --p2)
{
*p1 ^= *p2;
*p2 ^= *p1;
*p1 ^= *p2;
}
return str;
}
// Implementation of itoa()
char* itoa(int num, char* str, int base)
{
int i = 0;
bool isNegative = false;
/* Handle 0 explicitely, otherwise empty string is printed for 0 */
if (num == 0)
{
str[i++] = '0';
str[i] = '\0';
return str;
}
// In standard itoa(), negative numbers are handled only with
// base 10. Otherwise numbers are considered unsigned.
if (num < 0 && base == 10)
{
isNegative = true;
num = -num;
}
// Process individual digits
while (num != 0)
{
int rem = num % base;
str[i++] = (rem > 9)? (rem-10) + 'a' : rem + '0';
num = num/base;
}
// If number is negative, append '-'
if (isNegative)
str[i++] = '-';
str[i] = '\0'; // Append string terminator
// Reverse the string
reverse(str);
return str;
}
Another complete itoa() implementatiton: Reference Link
An itoa() usage example below (Reference Link):
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
int a=54325;
char buffer[20];
itoa(a,buffer,2); // here 2 means binary
printf("Binary value = %s\n", buffer);
itoa(a,buffer,10); // here 10 means decimal
printf("Decimal value = %s\n", buffer);
itoa(a,buffer,16); // here 16 means Hexadecimal
printf("Hexadecimal value = %s\n", buffer);
return 0;
}
if(InNumber == 0)
{
return TEXT("0");
}
const int32 CharsBufferSize = 64; // enought for int128 type
TCHAR ResultChars[CharsBufferSize];
int32 Number = InNumber;
// Defines Decreasing/Ascending ten-Digits to determine each digit in negative and positive numbers.
const TCHAR* DigitalChars = TEXT("9876543210123456789");
constexpr int32 ZeroCharIndex = 9; // Position of the ZERO character from the DigitalChars.
constexpr int32 Base = 10; // base system of the number.
// Convert each digit of the number to a digital char from the top down.
int32 CharIndex = CharsBufferSize - 1;
for(; Number != 0 && CharIndex > INDEX_NONE; --CharIndex)
{
const int32 CharToInsert = ZeroCharIndex + (Number % Base);
ResultChars[CharIndex] = DigitalChars[CharToInsert];
Number /= Base;
}
// Insert sign if is negative number to left of the digital chars.
if(InNumber < 0 && CharIndex > INDEX_NONE)
{
ResultChars[CharIndex] = L'-';
}
else
{
// return to the first digital char if is unsigned number.
++CharIndex;
}
// Get number of the converted chars and construct string to return.
const int32 ResultSize = CharsBufferSize - CharIndex;
return TString{&ResultChars[CharIndex], ResultSize};
Basically I'm writing a printf function for an dedicated system so I want to pass an optional number of arguments without using VA_ARGS macros. I knocked up a simple example and this block of code works:
#include <stdio.h>
void func(int i, ...);
int main(int argc, char *argv);
int main(int argc, char *argv) {
unsigned long long f = 6799000015ULL;
unsigned long long *g;
//g points to f
g = &f;
printf("natural: %llu in hex: %llX address: %x\n", *g, *g, g);
//put pointer onto stack
func(6, g, g);
return 0;
}
void func(int i, ...) {
unsigned long long *f;
//pop value off
f = *(&i + 1);
printf("address: %x natural: %llu in hex: %llX\n", f, *f, *f);
}
However the larger example I'm trying to transfer this to doesn't work.
(in the main function):
unsigned long long f = 6799000015ULL;
unsigned long long *g;
g = &f;
kprintf("ull test: 1=%U 2=%X 3=%x 4= 5=\n", g, g, g);
(my dodgy printf function that I'm having trouble with. It maybe worth pointing out
this code DOES work with ints, char strings or anyother % flags which are passed by
value and not pointer. The only difference between what did work and the unsigned
long longs is one is bigger, so I pass by value instead to ensure I don't increment
the &format+ args part wrongly. Does that make sense?)
void kprintf(char *format, ...)
{
char buffer[KPRINTF_BUFFER_SIZE];
int bpos = 0; /* position to write to in buffer */
int fpos = 0; /* position of char to print in format string */
char ch; /* current character being processed*/
/*
* We have a variable number of paramters so we
* have to increment from the position of the format
* argument.
*/
int arg_offset = 1;
/*
* Think this through Phill. &format = address of format on stack.
* &(format + 1) = address of argument after format on stack.
* void *p = &(format + arg_offset);
* kprintf("xxx %i %s", 32, "hello");
* memory would look like = [ 3, 32, 5, "xxx", 32, "hello" ]
* get to 32 via p = &(format + 1); (int)p (because the int is copied, not a pointer)
* get to hello via p = &(format + 2); (char*)p;
*/
void *arg;
unsigned long long *llu;
arg = (void*) (&format + arg_offset);
llu = (unsigned long long*) *(&format + arg_offset);
while (1)
{
ch = format[fpos++];
if (ch == '\0')
break;
if (ch != '%')
buffer[bpos++] = ch;
else
{
ch = format[fpos++];
if (ch == 's')
bpos += strcpy(&buffer[bpos], KPRINTF_BUFFER_SIZE - bpos, (char*)arg);
else if (ch == '%')
buffer[bpos++] = '%';
else if (ch == 'i')
bpos += int_to_str(&buffer[bpos], KPRINTF_BUFFER_SIZE - bpos, *((int*)arg));
else if (ch == 'x')
bpos += int_to_hex_str(&buffer[bpos], KPRINTF_BUFFER_SIZE - bpos, *((int*)arg));
else if (ch == 'o')
bpos += int_to_oct_str(&buffer[bpos], KPRINTF_BUFFER_SIZE - bpos, *((int*)arg));
else if (ch == 'X') {
//arg is expected to be a pointer we need to further dereference.
bpos += unsigned_long_long_to_hex(&buffer[bpos], KPRINTF_BUFFER_SIZE - bpos, *llu);
} else if (ch == 'U') {
bpos += unsigned_long_long_to_str(&buffer[bpos], KPRINTF_BUFFER_SIZE - bpos, *llu);
} else
{
puts("invalid char ");
putch(ch);
puts(" passed to kprintf\n");
}
arg_offset++;
arg = (void *)(&format + arg_offset);
llu = (unsigned long long*) *(&format + arg_offset);
}
}
buffer[bpos] = '\0';
puts(buffer);
}
(and the unsigned long long functions it goes on to call):
int unsigned_long_long_to_hex(char *buffer, int max_size, unsigned long long number)
{
return ull_number_to_str(buffer, max_size, number, BASE_HEX);
}
int unsigned_long_long_to_str(char *buffer, int max_size, unsigned long long number) {
return ull_number_to_str(buffer, max_size, number, BASE_DECIMAL);
}
int ull_number_to_str(char *buffer, int max_size, unsigned long long number, int base) {
int bufpos = 0;
unsigned int lo_byte = (unsigned int) number;
unsigned int hi_byte = (unsigned int) (number >> 32);
bufpos = number_to_str(buffer, max_size, lo_byte, base);
bufpos += number_to_str(buffer + bufpos, max_size, hi_byte, base);
return bufpos;
}
#define NUMERIC_BUFF_SIZE (11 * (ADDRESS_SIZE / 32))
int number_to_str(char *buffer, int max_size, int number, int base)
{
char *char_map = "0123456789ABCDEF";
int remain = 0;
char buff_stack[NUMERIC_BUFF_SIZE];
int stk_pnt = 0;
int bpos = 0;
/* with this method of parsing, the digits come out backwards */
do
{
if (stk_pnt > NUMERIC_BUFF_SIZE)
{
puts("Number has too many digits to be printed. Increasse NUMBERIC_BUFF_SIZE\n");
return 0;
}
remain = number % base;
number = number / base;
buff_stack[stk_pnt++] = char_map[remain];
} while (number > 0);
/* before writing...ensure we have enough room */
if (stk_pnt > max_size)
{
//error. do something?
puts("number_to_str passed number with too many digits to go into buffer\n");
//printf("error. stk_pnt > max_size (%d > %d)\n", stk_pnt, max_size);
return 0;
}
/* reorder */
while (stk_pnt > 0)
buffer[bpos++] = buff_stack[--stk_pnt];
return bpos;
}
Sorry guys, I can't see what I've done wrong. I appreciate this is a "wall of code" type scenario but hopefully someone can see what I've done wrong. I appreciate you probably dislike not using VA_ARGS but I don't understand why this technique shouldn't just work? And also, I'm linking with -nostdlib too. If someone can help I'd really appreciate it. Also, this isn't meant to be production quality code so if I lack some C fundamentals feel free to be constructive about it :-)
It's a bad idea to code this way. Use stdarg.h.
On the off chance (I presume this based on the name kprintf) that you're working on a hobby kernel or embedded project and looking to avoid using standard libraries, I recommend at least writing your own (architecture and compiler specific) set of stdarg macros that conform to the well-known interfaces and code against that. That way your code doesn't look like such a WTF by dereferencing past the address of the last argument.
You can make a va_list type that stores the last-known address, and your va_arg macro could appropriately align the sizeof of the type it's passed and advance the pointer accordingly. For most conventions I have worked on for x86, every type is promoted to 32 bits...
You have to read on the calling conventions for your platform, i.e. how on your target processor/OS function arguments are passed, and how registers are saved. Not all parameters are passed on stack. Depending on number of parameters and their types, many complex situations can arise.
I should add: if you want to manipulate the stack by hand as you are doing above, you need to do it in assembler, not in C. The C language follows a defined standard, and what you are doing above it not legal code (i.e., its meaning is not well-defined). As such, the compiler is allowed to do anything it wants with it, such as optimize it in weird ways unsuitable to your needs.