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<div class="moz-cite-prefix">Jeste jedna podotazka, stve me, ze
prekladac kazdy mezivysledek strka do pameti, napr. takto<br>
<br>
(786) amp = (ph1*ph1 + ph2*ph2 + ph3*ph3) * 2.0;
//-fno-math-errno<br>
080017E8 vldr s14, [r7, #56] ; 0x38<br>
080017EC vldr s15, [r7, #56] ; 0x38<br>
080017F0 vmul.f32 s14, s14, s15<br>
080017F4 vldr s13, [r7, #52] ; 0x34<br>
080017F8 vldr s15, [r7, #52] ; 0x34<br>
080017FC vmul.f32 s15, s13, s15<br>
08001800 vadd.f32 s14, s14, s15<br>
08001804 vldr s13, [r7, #48] ; 0x30<br>
08001808 vldr s15, [r7, #48] ; 0x30<br>
0800180C vmul.f32 s15, s13, s15<br>
08001810 vadd.f32 s15, s14, s15<br>
08001814 vadd.f32 s15, s15, s15<br>
<b>08001818 vstr s15, [r7, #44] ; 0x2c</b><b><br>
</b><b>(787) asm volatile ("vsqrt.f32 %0, %1" : "=w"
(amp) : "w" (amp) );</b><b><br>
</b><b>0800181C vldr s15, [r7, #44] ; 0x2c</b><b><br>
</b>08001820 vsqrt.f32 s15, s15<br>
08001824 vstr s15, [r7, #44] ; 0x2c<br>
<br>
program vypada takto:<br>
float amp;<br>
...<br>
amp = (ph1*ph1 + ph2*ph2 + ph3*ph3) * 2.0; <br>
asm volatile ("vsqrt.f32 %0, %1" : "=w" (amp) : "w" (amp)
);<br>
<br>
Optimalizace je na rychlost -Ofast<br>
<br>
Jde s tim neco delat?<br>
<br>
A jeste jedna podotazka, proc byva u inline assembleru volatile?
Bez toho to prelozi stejne v tomto pripade.<br>
<br>
<br>
Dne 11.02.2017 v 19:08 Jaroslav Buchta napsal(a):<br>
</div>
<blockquote
cite="mid:3718b20b-7400-6d7a-8409-f71942bc6285@hascomp.cz"
type="cite">Nevite, jak donutit gcc aby misto knihovni funkce
sqrtf pouzil instrukci vsqrt.f32 ?
<br>
<br>
Asi bych to tam dokazal nacpat assemblerem ale moc se mi to
nelibi.Ostatni FPU instrukce pouziva normalne.
<br>
<br>
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</blockquote>
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