How do I get the value of a certain bit from a byte or integer? The only similar answer that I've been able to find is for a specific character inside a string. I am trying to convert a binary number to a decimal number, and perhaps there is a much simpler way to do this, but I was thinking of this: multiplying 2^(position of integer from right) by either a 1 or 0, depending on the value of the integer at the position previously mentioned. Any tips?
NSString * binary = #"0011010";
long value = strtol([b UTF8String], NULL, 2);
There are multiways of obtaining the value of bit within a byte or integer. It all depends on your needs.
One way would be to use a mask with bitwise operators.
int result = sourceValue & 8; // 8 -> 0x00001000
// result non zero if the 4th bit from the right is ON.
You can also shift bits one by one and read, say, the right-most bit.
for (int i = 0; i < 8; i++)
NSLog(#"Bit %d is %#", i, (sourceValue % 2 == 0) ? #"OFF" : #"ON");
sourceValue = sourceValue >> 1; // shift bits to the right for next loop.
}
Or if you just want the text representation for an integer, you could let NSNumber do the work:
NSString* myString = [[NSNumber numberWithInt:sourceValue] stringValue];
Related
I'm trying to reverse a double value like this:
Input: 1020304050...... Output: 5040302010
the group of 2 digits remain in the same order. So 10 doesn't become 01. or 53 doesn't become 35.
The input will always have even number of digits, so pairing isn't an issue.
The 2 adjacent digits are actually a code number for a function. And I want to maintain that so I can apply that function again.
double temp = 0.0;
double Singlefilter=1;
double reverseString=0;
temp=filtersequence;
while (temp>0)
{
Singlefilter=fmod(temp, 100.00);
temp=temp/100;
reverseString=(reverseString+Singlefilter)*100;
NSLog(#"reversed string of filter %f",reverseString);
}
But I have no idea why this isn't working. This is generating randomly very very big values.
[This question has been replaced by Reverse a double value while maintaining 2 adjacent digits in same format]
You can do it like this:
#import <Foundation/Foundation.h>
#include "math.h"
void outputGroupReversed(double filtersequence)
{
double reverseString = 0.0;
double temp = filtersequence;
while (temp > 0.0)
{
double groupMultiplier = 100.0;
double singleFilter = fmod(temp, groupMultiplier);
temp = floor(temp / groupMultiplier);
reverseString = reverseString * groupMultiplier + singleFilter;
}
NSLog(#"reversed string of filter %f", reverseString);
}
int main(int argc, const char * argv[])
{
#autoreleasepool {
outputGroupReversed(1020304050.0);
}
return 0;
}
This code does not handle input with a fractional part correctly, though.
You're better off just converting it to a string and reversing it.
NSString *inputString = [#(input) stringValue]; // Eg 1230
NSMutableString *reversedString = [NSMutableString string];
NSInteger charIndex = [inputString length];
while (charIndex > 0) {
charIndex--;
NSRange subStrRange = NSMakeRange(charIndex, 1);
[reversedString appendString:[inputString substringWithRange:subStrRange]];
}
double result = [reversedString doubleValue]; // Eg 0321 -> 321
// Go back to NSString to get the missing length
NSString *resultString = [#(result) stringValue]; // Eg. 321
// Multiple by factors of 10 to add zeros
result *= exp(10, [inputString length] - [resultString length]); // 3210
NSLog(#"reversed value %f", result);
Reverse string method from this answer.
If you wish to store 2-digit decimal integers packed together as a single numeric value you would be better of using uint64_t - unsigned long 64 bit integers rather than double. That will store 9 pairs of two decimal digits precisely which appears to be one more than you need (you mention 16 digits in a comment).
As long as the numeric value of the packed pairs is not important, just that you can pack 8 2-digit decimal numbers (i.e. 0 -> 99) into a single numeric value, then you can do better. A 64-bit integer is 8 pairs of 2-hexadecimal digit numbers, or 8 8-bit bytes, so you can store 8 values 0 -> 99 one per byte. Now adding and extracting values becomes bit-shifts (>> & << operators) by 8 and bitwise-or (|) and bitwise-and (&). This at least makes it clear you are packing values in, which divide & remainder do not.
But there is another payoff, your "reverse" operation now becomes a single call to CFSwapInt64() which reverses the order of the bytes.
However having said the above, you really should look at your model and consider another data type for what you are doing - long gone are the days when programs had to pack multiple values into words to save space.
For example, why not just use a (C) array of 8-bit (uint8_t values[8]) integers? If you require you can place that in a struct and pass it around as a single value.
In my code, I'm dealing with an NSString that contains an NSNumber value. This NSNumber value could possibly be a repeating decimal number (e.x. 2.333333333e+06) that shortens to "2.333333" in a string format. It could also be a terminating number (e.x. 2.5), negative, or irrational number (2.398571892858...) (only dealing with decimals here)
I need to have a way to figure out if there are the repeating numbers in the string (or the NSNumber, if necessary). In my code, I would have no way to know what the repeating number would be, as it's a result of computations started by the user. I have tried this for loop (see below) that doesn't work the way I want it to, due to my inexperience with string indexing/ranges/lengths.
BOOL repeat = NO; //bool to check if repeating #
double repNum, tempNum; //run in for loop
NSString *repeating = [numVal stringValue]; //string that holds possible repeating #
for (int i = 3; i <= [repeating length]-3; i++) { //not sure about index/length here
if (i == 3) {
repNum = [repeating characterAtIndex:i];
}
tempNum = [repeating characterAtIndex:i];
if (tempNum == repNum) {
repeat = YES;
} else {
repeat = NO;
}
}
This code doesn't work as I'd like it to, mainly because I also have to account for negative dashes in the string and different amounts of numbers (13 1/3 vs. 1 1/3). I've used the modffunction to separate the integers from the decimals, but that hasn't worked well for me either.
Thank you in advance. Please let me know if I can clarify anything.
EDIT:
This code works with the finding of different solutions for polynomials (quadratic formula). Hope this helps put it into context. See here. (Example input)
NSNumber *firstPlusSolution, *secondMinusSolution;
NSString *pValueStr, *mValueStr;
firstPlusSolution = -(b) + sqrt(square(b) - (4)*(a)*(c)); //a, b, c: "user" provided
firstPlusSolution /= 2*(a);
secondMinusSolution = -(b) - sqrt(square(b) - 4*(a)*(c));
secondMinusSolution /= 2*(a);
pValueStr = [firstPlusSolution stringValue];
mValueStr = [secondMinusSolution stringValue];
if ([NSString doesString:pValueStr containCharacter:'.']) { //category method I implemented
double fractionPart, integerPart;
fractionPart = modf(firstPlusSolution, &integerPart);
NSString *repeating = [NSString stringWithFormat:#"%g", fractionPart];
int repNum, tempNum;
BOOL repeat = NO;
//do for loop and check for negatives, integers, etc.
}
if ([NSString doesString:mValueStr containCharacter'.']) {
//do above code
//do for loop and check again
}
Use C. Take the fractional part. Convert to a string with a known accuracy. If length of string indicates that last digits are missing, then it does not repeat. Use NSString-UTF8String to convert a string. Get rid of the last digit (may be rounding or actual floating point arithmetic error). Use function int strncmp ( const char * str1, const char * str2, size_t num ) to perform comparison within the string itself. If the result is 8 characters long and the last 2 characters match the first 2 characters, then shall the first 6 characters be considered repeating?
Assuming that fraction knowledge your desire:
• Possibility 1: Use fractions. Input fractions. Compute with fractions. Output fractions. Expand upon one of the many examples of a c++ fraction class if necessary and use it.
• Possibility 2: Choose an accuracy which is much less than double. Make a fraction from the result. Reduce the fraction allowing rounding based upon accuracy.
I suggest use not optimal but easy to write solution
Create NSMutableDictionary that will contain number as key and count of occurrence as value.
You can use componentsSeparatedByString: if numbers in string delimited by known symbol
In loop check valueForKey in dictionary and if need increase value
Last step is analyzing our dictionary and do anything you need with numbers
I've got a really large decimal number in an NSString, which is too large to fit into any variable including NSDecimal. I was doing the math manually, but if I can't fit the number into a variable then I can't be dividing it. So what would be a good way to convert the string?
Example Input: 423723487924398723478243789243879243978234
Output: 4DD361F5A772159224CE9EB0C215D2915FA
I was looking at the first answer here, but it's in C# and I don't know it's objective C equivalent.
Does anyone have any ideas that don't involve using an external library?
If this is all you need, it's not too hard to implement, especially if you're willing to use Objective-C++. By using Objective-C++, you can use a vector to manage memory, which simplifies the code.
Here's the interface we'll implement:
// NSString+BigDecimalToHex.h
#interface NSString (BigDecimalToHex)
- (NSString *)hexStringFromDecimalString;
#end
To implement it, we'll represent an arbitrary-precision non-negative integer as a vector of base-65536 digits:
// NSString+BigDecimalToHex.mm
#import "NSString+BigDecimalToHex.h"
#import <vector>
// index 0 is the least significant digit
typedef std::vector<uint16_t> BigInt;
The "hard" part is to multiply a BigInt by 10 and add a single decimal digit to it. We can very easily implement this as long multiplication with a preloaded carry:
static void insertDecimalDigit(BigInt &b, uint16_t decimalDigit) {
uint32_t carry = decimalDigit;
for (size_t i = 0; i < b.size(); ++i) {
uint32_t product = b[i] * (uint32_t)10 + carry;
b[i] = (uint16_t)product;
carry = product >> 16;
}
if (carry > 0) {
b.push_back(carry);
}
}
With that helper method, we're ready to implement the interface. First, we need to convert the decimal digit string to a BigInt by calling the helper method once for each decimal digit:
- (NSString *)hexStringFromDecimalString {
NSUInteger length = self.length;
unichar decimalCharacters[length];
[self getCharacters:decimalCharacters range:NSMakeRange(0, length)];
BigInt b;
for (NSUInteger i = 0; i < length; ++i) {
insertDecimalDigit(b, decimalCharacters[i] - '0');
}
If the input string is empty, or all zeros, then b is empty. We need to check for that:
if (b.size() == 0) {
return #"0";
}
Now we need to convert b to a hex digit string. The most significant digit of b is at the highest index. To avoid leading zeros, we'll handle that digit specially:
NSMutableString *hexString = [NSMutableString stringWithFormat:#"%X", b.back()];
Then we convert each remaining base-65536 digit to four hex digits, in order from most significant to least significant:
for (ssize_t i = b.size() - 2; i >= 0; --i) {
[hexString appendFormat:#"%04X", b[i]];
}
And then we're done:
return hexString;
}
You can find my full test program (to run as a Mac command-line program) in this gist.
I have a string which is a 13 digit number. I need to separate all the digits and find the sum of the individual digits. How can I do that?
I converted the string to NSArray like this :
NSArray *arrStrDigits = [str13DigitNumber componentsSeparatedByString:#""];
now I want to run a loop and get something like arrStrDigits[i]
I am new to Objective C :(. Please help me out!
Get the individual digits like this:
unichar digitChar = [str13DigitNumber characterAtIndex: someIndex];
// Should put in some validation that you have a digit here
int digit = digitChar - '0';
That just needs to go in a loop where you iterate someIndex from 0 to [str13DigitNumber length]
int total=0;
for(NSString *numberInString in arrStrDigits)
{
total+=[numberInString intValue];
}
Note: I am assuming you have int's in each position of your array.
Note 1: This answer is only related to what you ask (run a loop, nothing else).
Using foundation and cocoa frameworks on Mac, I am trying to convert an NSData object in humanly understandable number.
Let say the NSData object is an image of NPIXEL. I know the binary data are coded in big endian and represent 32 bit integer (to be more precise 32 bit two complements integer). I write the piece of code bellow to convert the NSData into an int array. But the value I got are completely wrong (this does not means the measurement are bad, I used a special software to read the data and the value given by the software are different from the one I got with my code).
-(int *) GetArrayOfLongInt
{
//Get the total number of element into the Array
int Nelements=[self NPIXEL];
//CREATE THE ARRAY
int array[Nelements];
//FILL THE ARRAY
int32_t intValue;
int32_t swappedValue;
double Value;
int Nbit = abs(BITPIX)*GCOUNT*(PCOUNT + Nelements); Nbit/=sizeof(int32_t);
int i=0;
int step=sizeof(int32_t);
for(int bit=0; bit < Nbit; bit+=step)
{
[Img getBytes:&swappedValue range:NSMakeRange(bit,step)];
intValue= NSSwapBigIntToHost(swappedValue);
array[i]=intValue;
i++;
}
return array;
}
This piece of code (with minor change) work perfectly when the binary data represent float or double, but I dont when it is 16,32 or 64 bit integer. I also tried changingNSSapBigIntToHostintoNSSwapLittleInttoHost`. I even tried with long, but the results is still the same, I got bad values. What wrong I am doing ?
PS: Some of the variable in my code are already set elsewhere in my program. BITPIX is the bit size of each pixel. In this case 32. GCOUNT is equal to 1, PCOUNT 0 and Nelements is the total number of pixel I should have in my image.
Returning a pointer to a local variable is a very bad idea. array could get overwritten at any time (or if you were to write through the pointer, you could corrupt the stack). You probably want something like:
// CREATE THE ARRAY
int *array = malloc(Nelements * sizeof(int));
Your algorithm seems a bit overkill, too. Why not just copy out the whole array from the NSData object, and then byteswap the entries in place? Something like:
int32_t length = [Img length];
int32_t *array = malloc(length);
[Img getBytes:array length:length];
for (i = 0; i < length/sizeof(int32_t); i++)
{
array[i] = NSSwapBigIntToHost(array[i]);
}