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A comment on Pretty.c. Parent comment

Re:Pretty.c by jdthedisciple on Thursday October 24, 2024 @03:06PM (#41938645)
what

    // FLT_EPSILON == 0.01
    equal(4.999, 5); // true
    4.999 == 5;      // false
am i missing?
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Re:Pretty.c by hmry on Thursday October 24, 2024 @03:52PM (#41939079)
FLT_EPSILON is not 0.01, it's 0.00000011920929.

But it's impossible to have a number that's 0.00000011920929 less than 5.0, or 0.00000011920929 more than 5.0, because the floats with enough magnitude to represent 5 are spaced further apart than that. Only numbers with magnitude < 2 are spaced close enough together.

In other words, the only 32-bit float that's within ±0.00000011920929 of 5.0 is 5.0 itself.

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Re:Pretty.c by jdthedisciple on Thursday October 24, 2024 @04:19PM (#41939314)
Oh you're right, thanks for the explanation!

Gotta research now where the 0.00000011920929 number comes from...

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Re:Pretty.c by masklinn on Thursday October 24, 2024 @04:27PM (#41939403)
It's the distance between 1.0 and the next representable float.
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Re:Pretty.c by jdthedisciple on Thursday October 24, 2024 @04:47PM (#41939585)
I got that but I am curious how to derive that number.

Is it representable as a non-trivial ratio of integers?

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Re:Pretty.c by hmry on Thursday October 24, 2024 @05:25PM (#41939960)
Good question! It's 1/(2**23), because 32 bit floats have 23 bits after the decimal point
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