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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_view_use_ssse3/" rel="canonical"><link href=../json_view_no_simd/ rel=prev><link href=../nlohmann_define_derived_type/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_VIEW_USE_SSSE3 - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_view_use_ssse3/" rel="canonical"><link href=../json_view_no_simd/ rel=prev><link href=../nlohmann_define_derived_type/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_VIEW_USE_SSSE3 - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#json_view_use_ssse3 class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> JSON_VIEW_USE_SSSE3 </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch 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</code></pre></div> <p>When defined on x86-64, the parser of <a href=../../basic_json_document/ ><code>basic_json_document</code></a> (<code><nlohmann/json_view.hpp></code>) validates non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> text in strings with SSSE3 without asking the CPU first.</p> <p>By default, the parser checks once at run time whether the CPU has SSSE3 (all x86-64 CPUs since about 2011 have it) and then validates non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> text 16 bytes at a time, using the "lookup4" algorithm of <a href="https://github.com/simdjson/simdjson">simdjson</a>; on CPUs without SSSE3, it validates one <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequence at a time. The vector check is compiled for SSSE3 with a function attribute (<abbr title="GNU Compiler Collection">GCC</abbr> 4.9 and later, Clang), so this needs no compiler option. With <abbr title="Microsoft Visual C++">MSVC</abbr>, the check uses <code>__cpuid</code>. On AArch64, the vector check uses NEON and is always on.</p> <p>Define the macro only together with a compiler option that enables SSSE3 (e.g. <code>-mssse3</code>, or <code>-march=</code> with a CPU that has it), and only for programs that run on such CPUs. It saves the check of the CPU, which costs little. The same input is accepted or rejected either way; only the speed of non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> text differs.</p> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>The macro selects between two definitions of the same inline functions. Whether it is defined is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_vssse3</code>, on every architecture), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.</p> </div> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">¶</a></h2> <p>By default, <code class=highlight><span class=n>JSON_VIEW_USE_SSSE3</span></code> is not defined.</p> <div class=highlight><pre><span></span><code><span class=cp>#undef JSON_VIEW_USE_SSSE3</span>
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</code></pre></div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>With CMake, for a program that only runs on CPUs with SSSE3:</p> <div class=highlight><pre><span></span><code><span class=nb>target_compile_definitions</span><span class=p>(</span><span class=s>your_target</span><span class=w> </span><span class=s>PRIVATE</span><span class=w> </span><span class=s>JSON_VIEW_USE_SSSE3</span><span class=p>)</span>
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<span class=nb>target_compile_options</span><span class=p>(</span><span class=s>your_target</span><span class=w> </span><span class=s>PRIVATE</span><span class=w> </span><span class=s>-mssse3</span><span class=p>)</span>
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