dec2flt: Move internal traits to better locations

`Float` and `FloatExt` are already used by both parsing and printing, so
move them out of `dec2flt` to a new module in `num::imp`. `Int` `Cast`
have the potential to be used more places in the future, so move them
there as well. `Lemire` is the only remaining trait; since it is small,
move it into the `dec2flt` root.

Author: tgross35

library/core/src/num/imp/dec2flt/decimal.rs

@@ -1,9 +1,10 @@
 //! Representation of a float as the significant digits and exponent.
 
-use crate::num::imp::dec2flt;
-use dec2flt::float::Lemire;
+use dec2flt::Lemire;
 use dec2flt::fpu::set_precision;
 
+use crate::num::imp::dec2flt;
+
 const INT_POW10: [u64; 16] = [
     1,
     10,

library/core/src/num/imp/dec2flt/lemire.rs

@@ -1,10 +1,9 @@
 //! Implementation of the Eisel-Lemire algorithm.
 
 use dec2flt::common::BiasedFp;
-use dec2flt::float::Float;
 use dec2flt::table::{LARGEST_POWER_OF_FIVE, POWER_OF_FIVE_128, SMALLEST_POWER_OF_FIVE};
 
-use crate::num::imp::dec2flt;
+use crate::num::imp::{Float, dec2flt};
 
 /// Compute w * 10^q using an extended-precision float representation.
 ///

library/core/src/num/imp/dec2flt/mod.rs

@@ -88,24 +88,104 @@
 )]
 
 use common::BiasedFp;
-use float::{FloatExt, Lemire};
 use lemire::compute_float;
 use parse::{parse_inf_nan, parse_number};
 use slow::parse_long_mantissa;
 
+use crate::f64;
 use crate::num::ParseFloatError;
 use crate::num::float_parse::FloatErrorKind;
+use crate::num::imp::FloatExt;
 
 mod common;
 pub mod decimal;
 pub mod decimal_seq;
 mod fpu;
-mod slow;
-mod table;
-// float is used in flt2dec, and all are used in unit tests.
-pub mod float;
 pub mod lemire;
 pub mod parse;
+mod slow;
+mod table;
+
+/// Extension to `Float` that are necessary for parsing using the Lemire method.
+///
+/// See the parent module's doc comment for why this is necessary.
+///
+/// Not intended for use outside of the `dec2flt` module.
+#[doc(hidden)]
+pub trait Lemire: FloatExt {
+    /// Maximum exponent for a fast path case, or `⌊(SIG_BITS+1)/log2(5)⌋`
+    // assuming FLT_EVAL_METHOD = 0
+    const MAX_EXPONENT_FAST_PATH: i64 = {
+        let log2_5 = f64::consts::LOG2_10 - 1.0;
+        (Self::SIG_TOTAL_BITS as f64 / log2_5) as i64
+    };
+
+    /// Minimum exponent for a fast path case, or `-⌊(SIG_BITS+1)/log2(5)⌋`
+    const MIN_EXPONENT_FAST_PATH: i64 = -Self::MAX_EXPONENT_FAST_PATH;
+
+    /// Maximum exponent that can be represented for a disguised-fast path case.
+    /// This is `MAX_EXPONENT_FAST_PATH + ⌊(SIG_BITS+1)/log2(10)⌋`
+    const MAX_EXPONENT_DISGUISED_FAST_PATH: i64 =
+        Self::MAX_EXPONENT_FAST_PATH + (Self::SIG_TOTAL_BITS as f64 / f64::consts::LOG2_10) as i64;
+
+    /// Maximum mantissa for the fast-path (`1 << 53` for f64).
+    const MAX_MANTISSA_FAST_PATH: u64 = 1 << Self::SIG_TOTAL_BITS;
+
+    /// Gets a small power-of-ten for fast-path multiplication.
+    fn pow10_fast_path(exponent: usize) -> Self;
+
+    /// Converts integer into float through an as cast.
+    /// This is only called in the fast-path algorithm, and therefore
+    /// will not lose precision, since the value will always have
+    /// only if the value is <= Self::MAX_MANTISSA_FAST_PATH.
+    fn from_u64(v: u64) -> Self;
+}
+
+#[cfg(target_has_reliable_f16)]
+impl Lemire for f16 {
+    fn pow10_fast_path(exponent: usize) -> Self {
+        #[allow(clippy::use_self)]
+        const TABLE: [f16; 8] = [1e0, 1e1, 1e2, 1e3, 1e4, 0.0, 0.0, 0.];
+        TABLE[exponent & 7]
+    }
+
+    #[inline]
+    fn from_u64(v: u64) -> Self {
+        debug_assert!(v <= Self::MAX_MANTISSA_FAST_PATH);
+        v as _
+    }
+}
+
+impl Lemire for f32 {
+    fn pow10_fast_path(exponent: usize) -> Self {
+        #[allow(clippy::use_self)]
+        const TABLE: [f32; 16] =
+            [1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10, 0., 0., 0., 0., 0.];
+        TABLE[exponent & 15]
+    }
+
+    #[inline]
+    fn from_u64(v: u64) -> Self {
+        debug_assert!(v <= Self::MAX_MANTISSA_FAST_PATH);
+        v as _
+    }
+}
+
+impl Lemire for f64 {
+    fn pow10_fast_path(exponent: usize) -> Self {
+        const TABLE: [f64; 32] = [
+            1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10, 1e11, 1e12, 1e13, 1e14, 1e15,
+            1e16, 1e17, 1e18, 1e19, 1e20, 1e21, 1e22, 0., 0., 0., 0., 0., 0., 0., 0., 0.,
+        ];
+        TABLE[exponent & 31]
+    }
+
+    #[inline]
+    fn from_u64(v: u64) -> Self {
+        debug_assert!(v <= Self::MAX_MANTISSA_FAST_PATH);
+        v as _
+    }
+}
 
 #[inline]
 pub(super) fn pfe_empty() -> ParseFloatError {

library/core/src/num/imp/dec2flt/parse.rs

@@ -2,9 +2,8 @@
 
 use dec2flt::common::{ByteSlice, is_8digits};
 use dec2flt::decimal::Decimal;
-use dec2flt::float::Float;
 
-use crate::num::imp::dec2flt;
+use crate::num::imp::{Float, dec2flt};
 
 const MIN_19DIGIT_INT: u64 = 100_0000_0000_0000_0000;
 

library/core/src/num/imp/dec2flt/slow.rs

@@ -2,9 +2,8 @@
 
 use dec2flt::common::BiasedFp;
 use dec2flt::decimal_seq::{DecimalSeq, parse_decimal_seq};
-use dec2flt::float::Float;
 
-use crate::num::imp::dec2flt;
+use crate::num::imp::{Float, dec2flt};
 
 /// Parse the significant digits and biased, binary exponent of a float.
 ///

library/core/src/num/imp/flt2dec/decoder.rs

@@ -1,7 +1,7 @@
 //! Decodes a floating-point value into individual parts and error ranges.
 
 use crate::num::FpCategory;
-use crate::num::imp::dec2flt::float::FloatExt;
+use crate::num::imp::FloatExt;
 
 /// Decoded unsigned finite value, such that:
 ///

library/core/src/num/imp/mod.rs

@@ -16,3 +16,6 @@ pub(crate) mod int_log10;
 pub(crate) mod int_sqrt;
 pub(crate) mod libm;
 pub(crate) mod overflow_panic;
+mod traits;
+
+pub use traits::{Float, FloatExt, Int};