CODEWITHSUNDEEP
floating-pointdoubleieee-754single-precision
Keith Grout
Keith Grout

Reputation: 909

Why is a float "single precision"?

I'm curious as to why the IEEE calls a 32-bit floating-point number single precision. Was it just a means of standardization, or does 'single' actually refer to a single 'something'.

Is it simply a standardized level? As in, precision level 1 (single), precision level 2 (double) and so on? I've searched all over and found a great deal about the history of floating point numbers, but nothing that quite answers my question.

Upvotes: 10

Views: 3288

Answers (4)

Patricia Shanahan
Patricia Shanahan

Reputation: 26185

In addition to the hardware view, on most systems the 32-bit format was used to implement the Fortran "real" type, and the 64 bit format to implement the Fortran "double precision" type.

Upvotes: 1

greg84
greg84

Reputation: 7599

The terminology "double" isn't quite correct, but it's close enough.

A 64 bit float uses 52 of the bits for the fraction instead of the 23 bits used for the fraction in a 32 bit float - it's not really "double", but it does use double the total bits.

The answer to this question is very interesting - you should give it a read.

Upvotes: 0

davnicwil
davnicwil

Reputation: 30957

I think it just refers to the number of bits used to represent the floating-point number, where single-precision uses 32 bits and double-precision uses 64 bits, i.e. double the number of bits.

Upvotes: 0

Dale Wilson
Dale Wilson

Reputation: 9434

On the machine I was working on at the time, a float occupied a single 36 bit register. A double occupied two 36 bit registers. The hardware had separate instructions for operating on the 1 register and 2 register versions of the number. I don't know for certain that that's where the terminology came from, but it's possible.

Upvotes: 12

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