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copied!<p>The C99 standard Annex F says:</p> <blockquote> <p>This annex specifies C language support for the <em>IEC 60559 floating-point standard. The IEC 60559 floating-point standard is specifically Binary floating-point arithmetic for microprocessor systems, second edition (IEC 60559:1989)</em>, previously designated <em>IEC 559:1989</em> and as <em>IEEE Standard for Binary Floating-Point Arithmetic (ANSI/IEEE 754−1985)</em>. <em>IEEE Standard for Radix-Independent Floating-Point Arithmetic (ANSI/IEEE 854−1987)</em> generalizes the binary standard to remove dependencies on radix and word length. IEC 60559 generally refers to the floating-point standard, as in IEC 60559 operation, IEC 60559 format, etc. An implementation that defines <code>__STDC_IEC_559__</code> shall conform to the specifications in this annex. Where a binding between the C language and IEC 60559 is indicated, the IEC 60559-specified behavior is adopted by reference, unless stated otherwise.</p> </blockquote> <p>And, immediately after,</p> <blockquote> <p>The C floating types match the IEC 60559 formats as follows:</p> <ul> <li>The <code>float</code> type matches the IEC 60559 single format.</li> <li>The <code>double</code> type matches the IEC 60559 double format.</li> </ul> </blockquote> <p>So, if IEC 60559 is basically IEEE 754-1985 and this specifies that 8 zero bytes mean 0.0 (as @David Heffernan said), this means that if you find <code>__STDC_IEC_559__</code> defined you can safely do a 0.0 initialization with <code>memset</code>.</p>

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