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diff --git a/third_party/rust/ryu/src/f2s_intrinsics.rs b/third_party/rust/ryu/src/f2s_intrinsics.rs
new file mode 100644
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+++ b/third_party/rust/ryu/src/f2s_intrinsics.rs
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+// 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 "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.
+
+use crate::d2s;
+
+pub const FLOAT_POW5_INV_BITCOUNT: i32 = d2s::DOUBLE_POW5_INV_BITCOUNT - 64;
+pub const FLOAT_POW5_BITCOUNT: i32 = d2s::DOUBLE_POW5_BITCOUNT - 64;
+
+#[cfg_attr(feature = "no-panic", inline)]
+fn pow5factor_32(mut value: u32) -> u32 {
+    let mut count = 0u32;
+    loop {
+        debug_assert!(value != 0);
+        let q = value / 5;
+        let r = value % 5;
+        if r != 0 {
+            break;
+        }
+        value = q;
+        count += 1;
+    }
+    count
+}
+
+// Returns true if value is divisible by 5^p.
+#[cfg_attr(feature = "no-panic", inline)]
+pub fn multiple_of_power_of_5_32(value: u32, p: u32) -> bool {
+    pow5factor_32(value) >= p
+}
+
+// Returns true if value is divisible by 2^p.
+#[cfg_attr(feature = "no-panic", inline)]
+pub fn multiple_of_power_of_2_32(value: u32, p: u32) -> bool {
+    // __builtin_ctz doesn't appear to be faster here.
+    (value & ((1u32 << p) - 1)) == 0
+}
+
+// It seems to be slightly faster to avoid uint128_t here, although the
+// generated code for uint128_t looks slightly nicer.
+#[cfg_attr(feature = "no-panic", inline)]
+fn mul_shift_32(m: u32, factor: u64, shift: i32) -> u32 {
+    debug_assert!(shift > 32);
+
+    // The casts here help MSVC to avoid calls to the __allmul library
+    // function.
+    let factor_lo = factor as u32;
+    let factor_hi = (factor >> 32) as u32;
+    let bits0 = m as u64 * factor_lo as u64;
+    let bits1 = m as u64 * factor_hi as u64;
+
+    let sum = (bits0 >> 32) + bits1;
+    let shifted_sum = sum >> (shift - 32);
+    debug_assert!(shifted_sum <= u32::max_value() as u64);
+    shifted_sum as u32
+}
+
+#[cfg_attr(feature = "no-panic", inline)]
+pub fn mul_pow5_inv_div_pow2(m: u32, q: u32, j: i32) -> u32 {
+    #[cfg(feature = "small")]
+    {
+        // The inverse multipliers are defined as [2^x / 5^y] + 1; the upper 64
+        // bits from the double lookup table are the correct bits for [2^x /
+        // 5^y], so we have to add 1 here. Note that we rely on the fact that
+        // the added 1 that's already stored in the table never overflows into
+        // the upper 64 bits.
+        let pow5 = unsafe { d2s::compute_inv_pow5(q) };
+        mul_shift_32(m, pow5.1 + 1, j)
+    }
+
+    #[cfg(not(feature = "small"))]
+    {
+        debug_assert!(q < d2s::DOUBLE_POW5_INV_SPLIT.len() as u32);
+        unsafe {
+            mul_shift_32(
+                m,
+                d2s::DOUBLE_POW5_INV_SPLIT.get_unchecked(q as usize).1 + 1,
+                j,
+            )
+        }
+    }
+}
+
+#[cfg_attr(feature = "no-panic", inline)]
+pub fn mul_pow5_div_pow2(m: u32, i: u32, j: i32) -> u32 {
+    #[cfg(feature = "small")]
+    {
+        let pow5 = unsafe { d2s::compute_pow5(i) };
+        mul_shift_32(m, pow5.1, j)
+    }
+
+    #[cfg(not(feature = "small"))]
+    {
+        debug_assert!(i < d2s::DOUBLE_POW5_SPLIT.len() as u32);
+        unsafe { mul_shift_32(m, d2s::DOUBLE_POW5_SPLIT.get_unchecked(i as usize).1, j) }
+    }
+}