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</pre><pre class="rust"><code><span class="comment">// Translated from C to Rust. The original C code can be found at
// https://github.com/ulfjack/ryu and carries the following license:
//
// Copyright 2018 Ulf Adams
//
// The contents of this file may be used under the terms of the Apache License,
// Version 2.0.
//
// (See accompanying file LICENSE-Apache or copy at
// http://www.apache.org/licenses/LICENSE-2.0)
//
// Alternatively, the contents of this file may be used under the terms of
// the Boost Software License, Version 1.0.
// (See accompanying file LICENSE-Boost or copy at
// https://www.boost.org/LICENSE_1_0.txt)
//
// Unless required by applicable law or agreed to in writing, this software
// is distributed on an &quot;AS IS&quot; BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.
</span><span class="kw">use </span><span class="kw">crate</span>::common::<span class="kw-2">*</span>;
<span class="kw">use </span><span class="kw">crate</span>::f2s_intrinsics::<span class="kw-2">*</span>;
<span class="kw">pub const </span>FLOAT_MANTISSA_BITS: u32 = <span class="number">23</span>;
<span class="kw">pub const </span>FLOAT_EXPONENT_BITS: u32 = <span class="number">8</span>;
<span class="kw">const </span>FLOAT_BIAS: i32 = <span class="number">127</span>;
<span class="kw">pub use </span><span class="kw">crate</span>::f2s_intrinsics::{FLOAT_POW5_BITCOUNT, FLOAT_POW5_INV_BITCOUNT};
<span class="comment">// A floating decimal representing m * 10^e.
</span><span class="kw">pub struct </span>FloatingDecimal32 {
<span class="kw">pub </span>mantissa: u32,
<span class="comment">// Decimal exponent&#39;s range is -45 to 38
// inclusive, and can fit in i16 if needed.
</span><span class="kw">pub </span>exponent: i32,
}
<span class="attribute">#[cfg_attr(feature = <span class="string">&quot;no-panic&quot;</span>, inline)]
</span><span class="kw">pub fn </span>f2d(ieee_mantissa: u32, ieee_exponent: u32) -&gt; FloatingDecimal32 {
<span class="kw">let </span>(e2, m2) = <span class="kw">if </span>ieee_exponent == <span class="number">0 </span>{
(
<span class="comment">// We subtract 2 so that the bounds computation has 2 additional bits.
</span><span class="number">1 </span>- FLOAT_BIAS - FLOAT_MANTISSA_BITS <span class="kw">as </span>i32 - <span class="number">2</span>,
ieee_mantissa,
)
} <span class="kw">else </span>{
(
ieee_exponent <span class="kw">as </span>i32 - FLOAT_BIAS - FLOAT_MANTISSA_BITS <span class="kw">as </span>i32 - <span class="number">2</span>,
(<span class="number">1u32 </span>&lt;&lt; FLOAT_MANTISSA_BITS) | ieee_mantissa,
)
};
<span class="kw">let </span>even = (m2 &amp; <span class="number">1</span>) == <span class="number">0</span>;
<span class="kw">let </span>accept_bounds = even;
<span class="comment">// Step 2: Determine the interval of valid decimal representations.
</span><span class="kw">let </span>mv = <span class="number">4 </span>* m2;
<span class="kw">let </span>mp = <span class="number">4 </span>* m2 + <span class="number">2</span>;
<span class="comment">// Implicit bool -&gt; int conversion. True is 1, false is 0.
</span><span class="kw">let </span>mm_shift = (ieee_mantissa != <span class="number">0 </span>|| ieee_exponent &lt;= <span class="number">1</span>) <span class="kw">as </span>u32;
<span class="kw">let </span>mm = <span class="number">4 </span>* m2 - <span class="number">1 </span>- mm_shift;
<span class="comment">// Step 3: Convert to a decimal power base using 64-bit arithmetic.
</span><span class="kw">let </span><span class="kw-2">mut </span>vr: u32;
<span class="kw">let </span><span class="kw-2">mut </span>vp: u32;
<span class="kw">let </span><span class="kw-2">mut </span>vm: u32;
<span class="kw">let </span>e10: i32;
<span class="kw">let </span><span class="kw-2">mut </span>vm_is_trailing_zeros = <span class="bool-val">false</span>;
<span class="kw">let </span><span class="kw-2">mut </span>vr_is_trailing_zeros = <span class="bool-val">false</span>;
<span class="kw">let </span><span class="kw-2">mut </span>last_removed_digit = <span class="number">0u8</span>;
<span class="kw">if </span>e2 &gt;= <span class="number">0 </span>{
<span class="kw">let </span>q = log10_pow2(e2);
e10 = q <span class="kw">as </span>i32;
<span class="kw">let </span>k = FLOAT_POW5_INV_BITCOUNT + pow5bits(q <span class="kw">as </span>i32) - <span class="number">1</span>;
<span class="kw">let </span>i = -e2 + q <span class="kw">as </span>i32 + k;
vr = mul_pow5_inv_div_pow2(mv, q, i);
vp = mul_pow5_inv_div_pow2(mp, q, i);
vm = mul_pow5_inv_div_pow2(mm, q, i);
<span class="kw">if </span>q != <span class="number">0 </span>&amp;&amp; (vp - <span class="number">1</span>) / <span class="number">10 </span>&lt;= vm / <span class="number">10 </span>{
<span class="comment">// We need to know one removed digit even if we are not going to loop below. We could use
// q = X - 1 above, except that would require 33 bits for the result, and we&#39;ve found that
// 32-bit arithmetic is faster even on 64-bit machines.
</span><span class="kw">let </span>l = FLOAT_POW5_INV_BITCOUNT + pow5bits(q <span class="kw">as </span>i32 - <span class="number">1</span>) - <span class="number">1</span>;
last_removed_digit =
(mul_pow5_inv_div_pow2(mv, q - <span class="number">1</span>, -e2 + q <span class="kw">as </span>i32 - <span class="number">1 </span>+ l) % <span class="number">10</span>) <span class="kw">as </span>u8;
}
<span class="kw">if </span>q &lt;= <span class="number">9 </span>{
<span class="comment">// The largest power of 5 that fits in 24 bits is 5^10, but q &lt;= 9 seems to be safe as well.
// Only one of mp, mv, and mm can be a multiple of 5, if any.
</span><span class="kw">if </span>mv % <span class="number">5 </span>== <span class="number">0 </span>{
vr_is_trailing_zeros = multiple_of_power_of_5_32(mv, q);
} <span class="kw">else if </span>accept_bounds {
vm_is_trailing_zeros = multiple_of_power_of_5_32(mm, q);
} <span class="kw">else </span>{
vp -= multiple_of_power_of_5_32(mp, q) <span class="kw">as </span>u32;
}
}
} <span class="kw">else </span>{
<span class="kw">let </span>q = log10_pow5(-e2);
e10 = q <span class="kw">as </span>i32 + e2;
<span class="kw">let </span>i = -e2 - q <span class="kw">as </span>i32;
<span class="kw">let </span>k = pow5bits(i) - FLOAT_POW5_BITCOUNT;
<span class="kw">let </span><span class="kw-2">mut </span>j = q <span class="kw">as </span>i32 - k;
vr = mul_pow5_div_pow2(mv, i <span class="kw">as </span>u32, j);
vp = mul_pow5_div_pow2(mp, i <span class="kw">as </span>u32, j);
vm = mul_pow5_div_pow2(mm, i <span class="kw">as </span>u32, j);
<span class="kw">if </span>q != <span class="number">0 </span>&amp;&amp; (vp - <span class="number">1</span>) / <span class="number">10 </span>&lt;= vm / <span class="number">10 </span>{
j = q <span class="kw">as </span>i32 - <span class="number">1 </span>- (pow5bits(i + <span class="number">1</span>) - FLOAT_POW5_BITCOUNT);
last_removed_digit = (mul_pow5_div_pow2(mv, (i + <span class="number">1</span>) <span class="kw">as </span>u32, j) % <span class="number">10</span>) <span class="kw">as </span>u8;
}
<span class="kw">if </span>q &lt;= <span class="number">1 </span>{
<span class="comment">// {vr,vp,vm} is trailing zeros if {mv,mp,mm} has at least q trailing 0 bits.
// mv = 4 * m2, so it always has at least two trailing 0 bits.
</span>vr_is_trailing_zeros = <span class="bool-val">true</span>;
<span class="kw">if </span>accept_bounds {
<span class="comment">// mm = mv - 1 - mm_shift, so it has 1 trailing 0 bit iff mm_shift == 1.
</span>vm_is_trailing_zeros = mm_shift == <span class="number">1</span>;
} <span class="kw">else </span>{
<span class="comment">// mp = mv + 2, so it always has at least one trailing 0 bit.
</span>vp -= <span class="number">1</span>;
}
} <span class="kw">else if </span>q &lt; <span class="number">31 </span>{
<span class="comment">// TODO(ulfjack): Use a tighter bound here.
</span>vr_is_trailing_zeros = multiple_of_power_of_2_32(mv, q - <span class="number">1</span>);
}
}
<span class="comment">// Step 4: Find the shortest decimal representation in the interval of valid representations.
</span><span class="kw">let </span><span class="kw-2">mut </span>removed = <span class="number">0i32</span>;
<span class="kw">let </span>output = <span class="kw">if </span>vm_is_trailing_zeros || vr_is_trailing_zeros {
<span class="comment">// General case, which happens rarely (~4.0%).
</span><span class="kw">while </span>vp / <span class="number">10 </span>&gt; vm / <span class="number">10 </span>{
vm_is_trailing_zeros &amp;= vm - (vm / <span class="number">10</span>) * <span class="number">10 </span>== <span class="number">0</span>;
vr_is_trailing_zeros &amp;= last_removed_digit == <span class="number">0</span>;
last_removed_digit = (vr % <span class="number">10</span>) <span class="kw">as </span>u8;
vr /= <span class="number">10</span>;
vp /= <span class="number">10</span>;
vm /= <span class="number">10</span>;
removed += <span class="number">1</span>;
}
<span class="kw">if </span>vm_is_trailing_zeros {
<span class="kw">while </span>vm % <span class="number">10 </span>== <span class="number">0 </span>{
vr_is_trailing_zeros &amp;= last_removed_digit == <span class="number">0</span>;
last_removed_digit = (vr % <span class="number">10</span>) <span class="kw">as </span>u8;
vr /= <span class="number">10</span>;
vp /= <span class="number">10</span>;
vm /= <span class="number">10</span>;
removed += <span class="number">1</span>;
}
}
<span class="kw">if </span>vr_is_trailing_zeros &amp;&amp; last_removed_digit == <span class="number">5 </span>&amp;&amp; vr % <span class="number">2 </span>== <span class="number">0 </span>{
<span class="comment">// Round even if the exact number is .....50..0.
</span>last_removed_digit = <span class="number">4</span>;
}
<span class="comment">// We need to take vr + 1 if vr is outside bounds or we need to round up.
</span>vr + ((vr == vm &amp;&amp; (!accept_bounds || !vm_is_trailing_zeros)) || last_removed_digit &gt;= <span class="number">5</span>)
<span class="kw">as </span>u32
} <span class="kw">else </span>{
<span class="comment">// Specialized for the common case (~96.0%). Percentages below are relative to this.
// Loop iterations below (approximately):
// 0: 13.6%, 1: 70.7%, 2: 14.1%, 3: 1.39%, 4: 0.14%, 5+: 0.01%
</span><span class="kw">while </span>vp / <span class="number">10 </span>&gt; vm / <span class="number">10 </span>{
last_removed_digit = (vr % <span class="number">10</span>) <span class="kw">as </span>u8;
vr /= <span class="number">10</span>;
vp /= <span class="number">10</span>;
vm /= <span class="number">10</span>;
removed += <span class="number">1</span>;
}
<span class="comment">// We need to take vr + 1 if vr is outside bounds or we need to round up.
</span>vr + (vr == vm || last_removed_digit &gt;= <span class="number">5</span>) <span class="kw">as </span>u32
};
<span class="kw">let </span>exp = e10 + removed;
FloatingDecimal32 {
exponent: exp,
mantissa: output,
}
}
</code></pre></div>
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