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</pre><pre class="rust ">
<span class="comment">// Copyright 2015 The Rust Project Developers. See the COPYRIGHT</span>
<span class="comment">// file at the top-level directory of this distribution and at</span>
<span class="comment">// http://rust-lang.org/COPYRIGHT.</span>
<span class="comment">//</span>
<span class="comment">// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or</span>
<span class="comment">// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license</span>
<span class="comment">// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your</span>
<span class="comment">// option. This file may not be copied, modified, or distributed</span>
<span class="comment">// except according to those terms.</span>
<span class="doccomment">//! Validating and decomposing a decimal string of the form:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! `(digits | digits? '.'? digits?) (('e' | 'E') ('+' | '-')? digits)?`</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! In other words, standard floating-point syntax, with two exceptions: No sign, and no</span>
<span class="doccomment">//! handling of "inf" and "NaN". These are handled by the driver function (super::dec2flt).</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Although recognizing valid inputs is relatively easy, this module also has to reject the</span>
<span class="doccomment">//! countless invalid variations, never panic, and perform numerous checks that the other</span>
<span class="doccomment">//! modules rely on to not panic (or overflow) in turn.</span>
<span class="doccomment">//! To make matters worse, all that happens in a single pass over the input.</span>
<span class="doccomment">//! So, be careful when modifying anything, and double-check with the other modules.</span>
<span class="kw">use</span> <span class="kw">super</span>::<span class="ident">num</span>;
<span class="kw">use</span> <span class="self">self</span>::<span class="ident">ParseResult</span>::{<span class="ident">Valid</span>, <span class="ident">ShortcutToInf</span>, <span class="ident">ShortcutToZero</span>, <span class="ident">Invalid</span>};
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">Sign</span> {
<span class="ident">Positive</span>,
<span class="ident">Negative</span>,
}
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>)]</span>
<span class="doccomment">/// The interesting parts of a decimal string.</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Decimal</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
<span class="kw">pub</span> <span class="ident">integral</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> [<span class="ident">u8</span>],
<span class="kw">pub</span> <span class="ident">fractional</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> [<span class="ident">u8</span>],
<span class="doccomment">/// The decimal exponent, guaranteed to have fewer than 18 decimal digits.</span>
<span class="kw">pub</span> <span class="ident">exp</span>: <span class="ident">i64</span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> <span class="ident">Decimal</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">integral</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> [<span class="ident">u8</span>], <span class="ident">fractional</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> [<span class="ident">u8</span>], <span class="ident">exp</span>: <span class="ident">i64</span>) <span class="op">-></span> <span class="ident">Decimal</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
<span class="ident">Decimal</span> { <span class="ident">integral</span>: <span class="ident">integral</span>, <span class="ident">fractional</span>: <span class="ident">fractional</span>, <span class="ident">exp</span>: <span class="ident">exp</span> }
}
}
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>)]</span>
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">ParseResult</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
<span class="ident">Valid</span>(<span class="ident">Decimal</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>),
<span class="ident">ShortcutToInf</span>,
<span class="ident">ShortcutToZero</span>,
<span class="ident">Invalid</span>,
}
<span class="doccomment">/// Check if the input string is a valid floating point number and if so, locate the integral</span>
<span class="doccomment">/// part, the fractional part, and the exponent in it. Does not handle signs.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">parse_decimal</span>(<span class="ident">s</span>: <span class="kw-2">&</span><span class="ident">str</span>) <span class="op">-></span> <span class="ident">ParseResult</span> {
<span class="kw">if</span> <span class="ident">s</span>.<span class="ident">is_empty</span>() {
<span class="kw">return</span> <span class="ident">Invalid</span>;
}
<span class="kw">let</span> <span class="ident">s</span> <span class="op">=</span> <span class="ident">s</span>.<span class="ident">as_bytes</span>();
<span class="kw">let</span> (<span class="ident">integral</span>, <span class="ident">s</span>) <span class="op">=</span> <span class="ident">eat_digits</span>(<span class="ident">s</span>);
<span class="kw">match</span> <span class="ident">s</span>.<span class="ident">first</span>() {
<span class="prelude-val">None</span> <span class="op">=></span> <span class="ident">Valid</span>(<span class="ident">Decimal</span>::<span class="ident">new</span>(<span class="ident">integral</span>, <span class="string">b""</span>, <span class="number">0</span>)),
<span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="string">b'e'</span>) <span class="op">|</span> <span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="string">b'E'</span>) <span class="op">=></span> {
<span class="kw">if</span> <span class="ident">integral</span>.<span class="ident">is_empty</span>() {
<span class="kw">return</span> <span class="ident">Invalid</span>; <span class="comment">// No digits before 'e'</span>
}
<span class="ident">parse_exp</span>(<span class="ident">integral</span>, <span class="string">b""</span>, <span class="kw-2">&</span><span class="ident">s</span>[<span class="number">1</span>..])
}
<span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="string">b'.'</span>) <span class="op">=></span> {
<span class="kw">let</span> (<span class="ident">fractional</span>, <span class="ident">s</span>) <span class="op">=</span> <span class="ident">eat_digits</span>(<span class="kw-2">&</span><span class="ident">s</span>[<span class="number">1</span>..]);
<span class="kw">if</span> <span class="ident">integral</span>.<span class="ident">is_empty</span>() <span class="op">&&</span> <span class="ident">fractional</span>.<span class="ident">is_empty</span>() <span class="op">&&</span> <span class="ident">s</span>.<span class="ident">is_empty</span>() {
<span class="kw">return</span> <span class="ident">Invalid</span>;
}
<span class="kw">match</span> <span class="ident">s</span>.<span class="ident">first</span>() {
<span class="prelude-val">None</span> <span class="op">=></span> <span class="ident">Valid</span>(<span class="ident">Decimal</span>::<span class="ident">new</span>(<span class="ident">integral</span>, <span class="ident">fractional</span>, <span class="number">0</span>)),
<span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="string">b'e'</span>) <span class="op">|</span> <span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="string">b'E'</span>) <span class="op">=></span> <span class="ident">parse_exp</span>(<span class="ident">integral</span>, <span class="ident">fractional</span>, <span class="kw-2">&</span><span class="ident">s</span>[<span class="number">1</span>..]),
_ <span class="op">=></span> <span class="ident">Invalid</span>, <span class="comment">// Trailing junk after fractional part</span>
}
}
_ <span class="op">=></span> <span class="ident">Invalid</span>, <span class="comment">// Trailing junk after first digit string</span>
}
}
<span class="doccomment">/// Carve off decimal digits up to the first non-digit character.</span>
<span class="kw">fn</span> <span class="ident">eat_digits</span>(<span class="ident">s</span>: <span class="kw-2">&</span>[<span class="ident">u8</span>]) <span class="op">-></span> (<span class="kw-2">&</span>[<span class="ident">u8</span>], <span class="kw-2">&</span>[<span class="ident">u8</span>]) {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">i</span> <span class="op">=</span> <span class="number">0</span>;
<span class="kw">while</span> <span class="ident">i</span> <span class="op"><</span> <span class="ident">s</span>.<span class="ident">len</span>() <span class="op">&&</span> <span class="string">b'0'</span> <span class="op"><=</span> <span class="ident">s</span>[<span class="ident">i</span>] <span class="op">&&</span> <span class="ident">s</span>[<span class="ident">i</span>] <span class="op"><=</span> <span class="string">b'9'</span> {
<span class="ident">i</span> <span class="op">+=</span> <span class="number">1</span>;
}
(<span class="kw-2">&</span><span class="ident">s</span>[..<span class="ident">i</span>], <span class="kw-2">&</span><span class="ident">s</span>[<span class="ident">i</span>..])
}
<span class="doccomment">/// Exponent extraction and error checking.</span>
<span class="kw">fn</span> <span class="ident">parse_exp</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>(<span class="ident">integral</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> [<span class="ident">u8</span>], <span class="ident">fractional</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> [<span class="ident">u8</span>], <span class="ident">rest</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> [<span class="ident">u8</span>]) <span class="op">-></span> <span class="ident">ParseResult</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
<span class="kw">let</span> (<span class="ident">sign</span>, <span class="ident">rest</span>) <span class="op">=</span> <span class="kw">match</span> <span class="ident">rest</span>.<span class="ident">first</span>() {
<span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="string">b'-'</span>) <span class="op">=></span> (<span class="ident">Sign</span>::<span class="ident">Negative</span>, <span class="kw-2">&</span><span class="ident">rest</span>[<span class="number">1</span>..]),
<span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="string">b'+'</span>) <span class="op">=></span> (<span class="ident">Sign</span>::<span class="ident">Positive</span>, <span class="kw-2">&</span><span class="ident">rest</span>[<span class="number">1</span>..]),
_ <span class="op">=></span> (<span class="ident">Sign</span>::<span class="ident">Positive</span>, <span class="ident">rest</span>),
};
<span class="kw">let</span> (<span class="kw-2">mut</span> <span class="ident">number</span>, <span class="ident">trailing</span>) <span class="op">=</span> <span class="ident">eat_digits</span>(<span class="ident">rest</span>);
<span class="kw">if</span> <span class="op">!</span><span class="ident">trailing</span>.<span class="ident">is_empty</span>() {
<span class="kw">return</span> <span class="ident">Invalid</span>; <span class="comment">// Trailing junk after exponent</span>
}
<span class="kw">if</span> <span class="ident">number</span>.<span class="ident">is_empty</span>() {
<span class="kw">return</span> <span class="ident">Invalid</span>; <span class="comment">// Empty exponent</span>
}
<span class="comment">// At this point, we certainly have a valid string of digits. It may be too long to put into</span>
<span class="comment">// an `i64`, but if it's that huge, the input is certainly zero or infinity. Since each zero</span>
<span class="comment">// in the decimal digits only adjusts the exponent by +/- 1, at exp = 10^18 the input would</span>
<span class="comment">// have to be 17 exabyte (!) of zeros to get even remotely close to being finite.</span>
<span class="comment">// This is not exactly a use case we need to cater to.</span>
<span class="kw">while</span> <span class="ident">number</span>.<span class="ident">first</span>() <span class="op">==</span> <span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="string">b'0'</span>) {
<span class="ident">number</span> <span class="op">=</span> <span class="kw-2">&</span><span class="ident">number</span>[<span class="number">1</span>..];
}
<span class="kw">if</span> <span class="ident">number</span>.<span class="ident">len</span>() <span class="op">>=</span> <span class="number">18</span> {
<span class="kw">return</span> <span class="kw">match</span> <span class="ident">sign</span> {
<span class="ident">Sign</span>::<span class="ident">Positive</span> <span class="op">=></span> <span class="ident">ShortcutToInf</span>,
<span class="ident">Sign</span>::<span class="ident">Negative</span> <span class="op">=></span> <span class="ident">ShortcutToZero</span>,
};
}
<span class="kw">let</span> <span class="ident">abs_exp</span> <span class="op">=</span> <span class="ident">num</span>::<span class="ident">from_str_unchecked</span>(<span class="ident">number</span>);
<span class="kw">let</span> <span class="ident">e</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">sign</span> {
<span class="ident">Sign</span>::<span class="ident">Positive</span> <span class="op">=></span> <span class="ident">abs_exp</span> <span class="kw">as</span> <span class="ident">i64</span>,
<span class="ident">Sign</span>::<span class="ident">Negative</span> <span class="op">=></span> <span class="op">-</span>(<span class="ident">abs_exp</span> <span class="kw">as</span> <span class="ident">i64</span>),
};
<span class="ident">Valid</span>(<span class="ident">Decimal</span>::<span class="ident">new</span>(<span class="ident">integral</span>, <span class="ident">fractional</span>, <span class="ident">e</span>))
}
</pre>
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