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copied!<p>This looks like an extreme case in the parser. The <code>XeY</code> format is described in <a href="http://cran.r-project.org/doc/manuals/R-lang.html#Literal-constants">Section 10.3.1: Literal Constants</a> of the <a href="http://cran.r-project.org/doc/manuals/R-lang.html">R Language Definition</a> and points to <code>?NumericConstants</code> for "up-to-date information on the currently accepted formats".</p> <p>The problem seems to be how the parser handles the exponent. The numeric constant is handled by <code>NumericValue</code> (line 4361 of <code>main/gram.c</code>), which calls <code>mkFloat</code> (line 4124 of <code>main/gram.c</code>), which calls <code>R_atof</code> (line 1584 of <code>main/util.c</code>), which calls <code>R_strtod4</code> (line 1461 of <code>main/util.c</code>). (All as of revision 60052.)</p> <p>Line 1464 of <code>main/utils.c</code> shows <code>expn</code> declared as <code>int</code> and it will overflow at line 1551 if the exponent is too large. The signed integer overflow causes undefined behavior.</p> <p>For example, the code below produces values for exponents < 308 or so and <code>Inf</code> for exponents > 308.</p> <pre><code>const <- paste0("1e",2^(1:31)-2) for(n in const) print(eval(parse(text=n))) </code></pre> <p>You can see the undefined behavior for exponents > 2^31 (R hangs for an exponent = 2^31):</p> <pre><code>const <- paste0("1e",2^(31:61)+1) for(n in const) print(eval(parse(text=n))) </code></pre> <p>I doubt this will get any attention from R-core because R can only store numeric values between about 2e-308 to 2e+308 (see <code>?double</code>) and this number is <em>way</em> beyond that.</p>

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