Print int128 value from struct

Question

I have this int128 that is a tuple of 2 64-bit integers:

struct int128 {

    uint64_t    left;
    int64_t     right;
};

I know how to make basic arithmetic like multiply, addition and subtraction, but I don't know how to print the current signed value in C.

Can someone show me please how to do that?

I'm going to guess you need to write a bunch of functions to do that. — tadman, Mar 27 '21 at 00:53
There are many [good C reference books](https://stackoverflow.com/questions/562303/the-definitive-c-book-guide-and-list) to learn from. — tadman, Mar 27 '21 at 01:17
How will you print an `int` value without using `printf()` family? — MikeCAT, Mar 27 '21 at 02:17
Do you know how to make a division with remainder in your 128 bit datatype? if so, you can extract decimal digits dividing by 10 — Will, Mar 27 '21 at 03:04
typically those are called the high and low significant or most and least significant parts, not left and right — phuclv, Mar 27 '21 at 10:45
Does this answer your question? [How to convert a 128-bit integer to a decimal ascii string in C?](https://stackoverflow.com/questions/8023414/how-to-convert-a-128-bit-integer-to-a-decimal-ascii-string-in-c) — phuclv, Mar 27 '21 at 10:46
@Will Yes i made division arithmetic. Can you provide sample code to try? — sakdkjkj jjsdjds, Mar 27 '21 at 11:21
@phuclv Thank you, but the code does not work with negative values.. — sakdkjkj jjsdjds, Mar 27 '21 at 12:06

score 0 · Accepted Answer · answered Mar 29 '21 at 18:54

Assuming you have the following function:

int64_t divideRem(struct int128 *number, int64_t divisor);

That divides number / divisor, setting the division result on number, and returns the remainder of the division.

You could use a recursive implementation:

printInt128rec(struct int128 *number) {
  int64_t rem;
  rem = divideRem(number, 10);
  if( cmpInt128(number, 0) != 0 ) { /* compares number with 0 */
    printInt128rec(number);
  }
  printf("%d", rem);
}

Your main print function should copy the number to avoid modifications, and check for negatives:

printInt128(struct int128 *number) {
  struct int128 copy = *number;
  if( cmpInt128(&copy, 0) < 0 ) {  /* number is negative */
    printf("-");
    becomePositive(&copy); /* copy = abs (number ) */
  }
  printInt128rec(&copy);
}

Now you may call printInt128 to print your numbers. Notice that I used several other functions that operates between an int128 integer and an int64. If you know how to make 128 bits arithmetics these should be easier to implement.

Thank you ! - i did the same before i saw your post. Happy that your solution confirm that i did the right thing :) - once again thank you! — sakdkjkj jjsdjds, Mar 30 '21 at 07:37

Print int128 value from struct

1 Answers1

Linked