Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 83 insertions, 0 deletions

diff --git a/third_party/rust/minimal-lexical/src/number.rs b/third_party/rust/minimal-lexical/src/number.rs
new file mode 100644
index 0000000000..5981f9dd79
--- /dev/null
+++ b/third_party/rust/minimal-lexical/src/number.rs
@@ -0,0 +1,83 @@
+//! Representation of a float as the significant digits and exponent.
+//!
+//! This is adapted from [fast-float-rust](https://github.com/aldanor/fast-float-rust),
+//! a port of [fast_float](https://github.com/fastfloat/fast_float) to Rust.
+
+#![doc(hidden)]
+
+#[cfg(feature = "nightly")]
+use crate::fpu::set_precision;
+use crate::num::Float;
+
+/// Representation of a number as the significant digits and exponent.
+///
+/// This is only used if the exponent base and the significant digit
+/// radix are the same, since we need to be able to move powers in and
+/// out of the exponent.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+pub struct Number {
+    /// The exponent of the float, scaled to the mantissa.
+    pub exponent: i32,
+    /// The significant digits of the float.
+    pub mantissa: u64,
+    /// If the significant digits were truncated.
+    pub many_digits: bool,
+}
+
+impl Number {
+    /// Detect if the float can be accurately reconstructed from native floats.
+    #[inline]
+    pub fn is_fast_path<F: Float>(&self) -> bool {
+        F::MIN_EXPONENT_FAST_PATH <= self.exponent
+            && self.exponent <= F::MAX_EXPONENT_DISGUISED_FAST_PATH
+            && self.mantissa <= F::MAX_MANTISSA_FAST_PATH
+            && !self.many_digits
+    }
+
+    /// The fast path algorithmn using machine-sized integers and floats.
+    ///
+    /// This is extracted into a separate function so that it can be attempted before constructing
+    /// a Decimal. This only works if both the mantissa and the exponent
+    /// can be exactly represented as a machine float, since IEE-754 guarantees
+    /// no rounding will occur.
+    ///
+    /// There is an exception: disguised fast-path cases, where we can shift
+    /// powers-of-10 from the exponent to the significant digits.
+    pub fn try_fast_path<F: Float>(&self) -> Option<F> {
+        // The fast path crucially depends on arithmetic being rounded to the correct number of bits
+        // without any intermediate rounding. On x86 (without SSE or SSE2) this requires the precision
+        // of the x87 FPU stack to be changed so that it directly rounds to 64/32 bit.
+        // The `set_precision` function takes care of setting the precision on architectures which
+        // require setting it by changing the global state (like the control word of the x87 FPU).
+        #[cfg(feature = "nightly")]
+        let _cw = set_precision::<F>();
+
+        if self.is_fast_path::<F>() {
+            let max_exponent = F::MAX_EXPONENT_FAST_PATH;
+            Some(if self.exponent <= max_exponent {
+                // normal fast path
+                let value = F::from_u64(self.mantissa);
+                if self.exponent < 0 {
+                    // SAFETY: safe, since the `exponent <= max_exponent`.
+                    value / unsafe { F::pow_fast_path((-self.exponent) as _) }
+                } else {
+                    // SAFETY: safe, since the `exponent <= max_exponent`.
+                    value * unsafe { F::pow_fast_path(self.exponent as _) }
+                }
+            } else {
+                // disguised fast path
+                let shift = self.exponent - max_exponent;
+                // SAFETY: safe, since `shift <= (max_disguised - max_exponent)`.
+                let int_power = unsafe { F::int_pow_fast_path(shift as usize, 10) };
+                let mantissa = self.mantissa.checked_mul(int_power)?;
+                if mantissa > F::MAX_MANTISSA_FAST_PATH {
+                    return None;
+                }
+                // SAFETY: safe, since the `table.len() - 1 == max_exponent`.
+                F::from_u64(mantissa) * unsafe { F::pow_fast_path(max_exponent as _) }
+            })
+        } else {
+            None
+        }
+    }
+}