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    <p>Took the liberty to assume a few things explained below, but this kind of code (untested, may require a few modifications) should provide a good speedup compared to naive non-NEON version:</p> <pre><code>#include &lt;arm_neon.h&gt; #include &lt;stdint.h&gt; void convert(const restrict *uint16_t input, // the buffer to convert restrict *uint8_t output, // the buffer in which to store result int sz) { // their (common) size /* Assuming the buffer size is a multiple of 8 */ for (int i = 0; i &lt; sz; i += 8) { // Load a vector of 8 16-bit values: uint16x8_t v = vld1q_u16(buf+i); // Shift it by 4 to the right, narrowing it to 8 bit values. uint8x8_t shifted = vshrn_n_u16(v, 4); // Store it in output buffer vst1_u8(output+i, shifted); } } </code></pre> <p>Things I assumed here:</p> <ul> <li>that you're working with unsigned values. If it's not the case, it will be easy to adapt anyway (<code>uint*</code> -> <code>int*</code>, <code>*_u8</code>-><code>*_s8</code> and <code>*_u16</code>-><code>*_s16</code>)</li> <li>as the values are loaded 8 by 8, I assumed the buffer length was a multiple of 8 to avoid edge cases. If that's not the case, you should probably pad it artificially to a multiple of 8.</li> </ul> <p>Finally, the 2 resource pages used from the NEON documentation:</p> <ul> <li>about <a href="http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0348c/BABDCGGF.html" rel="nofollow">loads and stores</a> of vectors.</li> <li>about <a href="http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0348c/BABIBBJG.html" rel="nofollow">shifting vectors</a>.</li> </ul> <p>Hope this helps!</p>
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    1. PONEON acceleration for 12-bit to 8-bit
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    1. COyou don't need the q flag to be set unless you also set the r flag. nothing to saturate here.
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      1. USJake 'Alquimista' LEE
    2. COTrue, that's a bad copy-paste from the NEON documentation! Fixed it.
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    3. COThank you. I will do some tests. I am trying to include such code into a Qt 4.8 application, and need to remove the "const restrict". The buf+i was changed to input+i. Data is 12-bit unsigned into 16-bit and now shifted into 8-bit unsigned.
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      1. USbhamadicharef
 

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