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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="ZSTD_CCtx_refPrefix() : Requires v1.4.0+ Reference a prefix (single-usage dictionary) for next compressed frame. A prefix is only used once. Tables are discarded at end of frame (ZSTD_e_end). Decompression will need same prefix to properly regenerate data. Compressing with a prefix is similar in outcome as performing a diff and compressing it, but performs much faster, especially during decompression (compression speed is tunable with compression level). @result : 0, or an error code (which can be tested with ZSTD_isError()). Special: Adding any prefix (including NULL) invalidates any previous prefix or dictionary Note 1 : Prefix buffer is referenced. It must outlive compression. Its content must remain unmodified during compression. Note 2 : If the intention is to diff some large src data blob with some prior version of itself, ensure that the window size is large enough to contain the entire source. See ZSTD_c_windowLog. Note 3 : Referencing a prefix involves building tables, which are dependent on compression parameters. It’s a CPU consuming operation, with non-negligible impact on latency. If there is a need to use the same prefix multiple times, consider loadDictionary instead. Note 4 : By default, the prefix is interpreted as raw content (ZSTD_dct_rawContent). Use experimental ZSTD_CCtx_refPrefix_advanced() to alter dictionary interpretation."><meta name="keywords" content="rust, rustlang, rust-lang, ZSTD_CCtx_refPrefix"><title>ZSTD_CCtx_refPrefix in zstd_sys - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" type="text/css" href="../normalize.css"><link rel="stylesheet" type="text/css" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../ayu.css" disabled><link rel="stylesheet" type="text/css" href="../dark.css" disabled><link rel="stylesheet" type="text/css" href="../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../storage.js"></script><script src="../crates.js"></script><script defer src="../main.js"></script>
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</a><div class="sidebar-elems"><h2 class="location">Other items in<br><a href="index.html">zstd_sys</a></h2><div id="sidebar-vars" data-name="ZSTD_CCtx_refPrefix" data-ty="fn" data-relpath=""></div><script defer src="sidebar-items.js"></script></div></nav><main><div class="width-limiter"><div class="sub-container"><a class="sub-logo-container" href="../zstd_sys/index.html"><img class="rust-logo" src="../rust-logo.png" alt="logo"></a><nav class="sub"><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu" title="themes"><img width="18" height="18" alt="Pick another theme!" src="../brush.svg"></button><div id="theme-choices" role="menu"></div></div><form class="search-form"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><button type="button" id="help-button" title="help">?</button><a id="settings-menu" href="../settings.html" title="settings"><img width="18" height="18" alt="Change settings" src="../wheel.svg"></a></div></form></nav></div><section id="main-content" class="content"><h1 class="fqn"><span class="in-band">Function <a href="index.html">zstd_sys</a>::<wbr><a class="fn" href="#">ZSTD_CCtx_refPrefix</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../clipboard.svg" width="19" height="18" alt="Copy item path"></button></span><span class="out-of-band"><span id="render-detail"><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span><a class="srclink" href="../src/zstd_sys/bindings_std.rs.html#858-862" title="goto source code">[src]</a></span></h1><div class="docblock item-decl"><pre class="rust fn"><code>pub unsafe extern "C" fn ZSTD_CCtx_refPrefix(<br> cctx: <a class="primitive" href="https://doc.rust-lang.org/1.59.0/std/primitive.pointer.html">*mut </a><a class="type" href="type.ZSTD_CCtx.html" title="type zstd_sys::ZSTD_CCtx">ZSTD_CCtx</a>, <br> prefix: <a class="primitive" href="https://doc.rust-lang.org/1.59.0/std/primitive.pointer.html">*const </a><a class="enum" href="https://doc.rust-lang.org/1.59.0/core/ffi/enum.c_void.html" title="enum core::ffi::c_void">c_void</a>, <br> prefixSize: <a class="primitive" href="https://doc.rust-lang.org/1.59.0/std/primitive.usize.html">usize</a><br>) -> <a class="primitive" href="https://doc.rust-lang.org/1.59.0/std/primitive.usize.html">usize</a></code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>ZSTD_CCtx_refPrefix() : Requires v1.4.0+
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Reference a prefix (single-usage dictionary) for next compressed frame.
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A prefix is <strong>only used once</strong>. Tables are discarded at end of frame (ZSTD_e_end).
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Decompression will need same prefix to properly regenerate data.
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Compressing with a prefix is similar in outcome as performing a diff and compressing it,
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but performs much faster, especially during decompression (compression speed is tunable with compression level).
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@result : 0, or an error code (which can be tested with ZSTD_isError()).
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Special: Adding any prefix (including NULL) invalidates any previous prefix or dictionary
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Note 1 : Prefix buffer is referenced. It <strong>must</strong> outlive compression.
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Its content must remain unmodified during compression.
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Note 2 : If the intention is to diff some large src data blob with some prior version of itself,
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ensure that the window size is large enough to contain the entire source.
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See ZSTD_c_windowLog.
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Note 3 : Referencing a prefix involves building tables, which are dependent on compression parameters.
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It’s a CPU consuming operation, with non-negligible impact on latency.
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If there is a need to use the same prefix multiple times, consider loadDictionary instead.
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Note 4 : By default, the prefix is interpreted as raw content (ZSTD_dct_rawContent).
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Use experimental ZSTD_CCtx_refPrefix_advanced() to alter dictionary interpretation.</p>
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