What's bigger than a long double?

Question

So I'm trying to find the result of 1.25 ÷ (2 ✕ 10^-12). I first tried doing it with python, but the result was too big it returned a negative number. So I tried doing it in C, using a long double, but it's still not enough.

PS. I'm using GCC v9.2.1 on Linux Ubuntu

6.25 x 10^11 doesn't seem that big, and can be represented exactly in a `double`. — Ian Abbott, Jan 09 '20 at 10:34

score 1 · Answer 1 · answered Jan 09 '20 at 10:52

1

Don't see anything wrong with python:

>>> 1.25 / (2 * 10**-12)
625000000000.0

answered Jan 09 '20 at 10:52

lenik

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Why do I get `-0.0390625` when I replace `**` with `^` though? – VirtualCode Jan 09 '20 at 11:19
use 2e-12 instead of `2 * 10**-12` – phuclv Jan 09 '20 at 11:34
@VirtualCode because `^` is XOR operation ? – lenik Jan 10 '20 at 02:18
@lenik Yeah thanks, @Blaze told me above. But don't some languages have `^` as an exponentiation operator, though? – VirtualCode Jan 11 '20 at 11:57
@VirtualCode I've never heard of any language using `÷` and `✕` =) – lenik Jan 12 '20 at 01:50
1

@lenik Take a look at APL. – Patricia Shanahan Jan 13 '20 at 00:00

Blaze · Accepted Answer · 2020-01-09T11:31:52.900

-1

long long won't go bigger than a long double, but for your calculation, it's fine:

#include "stdio.h"
int main(){
    long long a = 1.25 / 2e-12;
    printf("%lld\n", a);
}

This prints 625000000000 for me.

edited Jan 09 '20 at 11:31

answered Jan 09 '20 at 10:39

Blaze

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Why doesn't it give the same with result when I use `^`? – VirtualCode Jan 09 '20 at 11:20
@VirtualCode that's because the `^` operator isn't for exponentiation, but [bitwise XOR](https://www.geeksforgeeks.org/bitwise-operators-in-c-cpp/). `10 ^ 12` is `6`, because their bit pattern are `1010` respectively `1100`, so xor'd they are `0110`, which is the bit pattern for `6`. – Blaze Jan 09 '20 at 11:24
`2 ✕ 10^-12 = 2e-12`, not `2 * 10e-12`. And the expression is done in double precision. To do in `long double` use `1.25L/2e-12L` – phuclv Jan 09 '20 at 11:30
This is not a correct method. `2e-12` or `2e-12l` may round up when converted from decimal to the internal floating-point format, the division may round down, and then the result will not be `625000000000`. – Eric Postpischil Jan 09 '20 at 18:15

What's bigger than a long double?

2 Answers2