StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

POCoercing float into unsigned char on ARM vs. Intel
text
Body
copied!<p>When I run the following C code on an Intel machine...</p> <pre><code>float f = -512; unsigned char c; while ( f < 513 ) { c = f; printf( "%f -> %d\n", f, c ); f += 64; } </code></pre> <p>...the output is as follows:</p> <pre><code>-512.000000 -> 0 -448.000000 -> 64 -384.000000 -> 128 -320.000000 -> 192 -256.000000 -> 0 -192.000000 -> 64 -128.000000 -> 128 -64.000000 -> 192 0.000000 -> 0 64.000000 -> 64 128.000000 -> 128 192.000000 -> 192 256.000000 -> 0 320.000000 -> 64 384.000000 -> 128 448.000000 -> 192 512.000000 -> 0 </code></pre> <p>However, when I run the same code on an ARM device (in my case an iPad), the results are quite different:</p> <pre><code>-512.000000 -> 0 -448.000000 -> 0 -384.000000 -> 0 -320.000000 -> 0 -256.000000 -> 0 -192.000000 -> 0 -128.000000 -> 0 -64.000000 -> 0 0.000000 -> 0 64.000000 -> 64 128.000000 -> 128 192.000000 -> 192 256.000000 -> 0 320.000000 -> 64 384.000000 -> 128 448.000000 -> 192 512.000000 -> 0 </code></pre> <p>As you can imagine, this sort of difference can introduce <em>horrible</em> bugs in cross-platform projects. My questions are:</p> <ol> <li><p>Was I wrong to assume that coercing a float into an unsigned char would yield the same results on all platforms?</p></li> <li><p>Could his be a compiler issue?</p></li> <li><p>Is there an elegant workaround?</p></li> </ol>

Querying!

Guidance

An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload