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Date: Wed, 19 Nov 2014 23:06:33 -0500
From: Rich Felker <>
Subject: Re: question about malloc's bin_index

On Wed, Nov 19, 2014 at 06:43:23PM -0800, Weiming Zhao wrote:
> Hi,
> I'm trying to use MUSL on a hardware without floating point unit, however,
> the "union" in the bin_index brings some issues.
> I'm using -mgeneral-regs-only and gcc refuses to compile it due to the
> floating point conversion.

This is odd. It should use soft-float if there's no fpu.

> I'm wondering what's the purpose of the union? How should I rewrite it to
> use integer only?

The value we want, for categorizing sizes into bins, is exactly the
floating point exponent and first 2 bits of the mantissa. It's
basically a sort of base-2 log with 4 linear steps between successive
logarithmic-scale points. I think nsz has an integer-only version of
this code that might be useful; it performs mildly better on archs
without fpu and mildly worse on ones with fpu and it's somewhat larger
(but of course not as large as soft-float code). I'll see if I can
find a copy or if he can post it.


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