Databases
StackOverflow2013
Postsdbo
POMost efficient way to convert 8 hex chars into a 4-uint8_t array?
Body
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POMost efficient way to convert 8 hex chars into a 4-uint8_t array?
    text
    copied!<p>I have a <code>const char*</code>, pointing to an array of 8 characters (that may be a part of a larger string), containing a hexadecimal value. I need a function that converts those chars into an array of 4 <code>uint8_t</code>, where the two first characters in the source array will become the first element in the target array, and so on. For example, if I have this</p> <pre><code>const char* s = "FA0BD6E4"; </code></pre> <p>I want it converted to </p> <pre><code>uint8_t i[4] = {0xFA, 0x0B, 0xD6, 0xE4}; </code></pre> <p>Currently, I have these functions:</p> <pre><code>inline constexpr uint8_t HexChar2UInt8(char h) noexcept { return static_cast&lt;uint8_t&gt;((h &amp; 0xF) + (((h &amp; 0x40) &gt;&gt; 3) | ((h &amp; 0x40) &gt;&gt; 6))); } inline constexpr uint8_t HexChars2UInt8(char h0, char h1) noexcept { return (HexChar2UInt8(h0) &lt;&lt; 4) | HexChar2UInt8(h1); } inline constexpr std::array&lt;uint8_t, 4&gt; HexStr2UInt8(const char* in) noexcept { return {{ HexChars2UInt8(in[0], in[1]), HexChars2UInt8(in[2], in[3]), HexChars2UInt8(in[4], in[5]), HexChars2UInt8(in[6], in[7]) }}; } </code></pre> <p>Here's what it will look like where I call it from:</p> <pre><code>const char* s = ...; // the source string std::array&lt;uint8_t, 4&gt; a; // I need to place the resulting value in this array a = HexStr2UInt8(s); // the function call does not have to look like this </code></pre> <p>What I'm wondering, is there any more efficient (and portable) way do do this? For example, is returning a <code>std::array</code> a good thing to do, or should I pass a <code>dst</code> pointer to <code>HexChars2UInt8</code>? Or are there any other way to improve my function(s)?</p> <p>The main reason I'm asking this is because I will likely need to optimize this at some point, and it will be problematic if the API (the function prototype) is changed in the future.</p>
 

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