Auto merge of #41302 - rkruppe:dec2flt-assoc-consts, r=BurntSushi

Use associated constants in core::num::dec2flt

Author: bors

src/libcore/lib.rs

@@ -70,6 +70,7 @@
 #![feature(allow_internal_unstable)]
 #![feature(asm)]
 #![feature(associated_type_defaults)]
+#![feature(associated_consts)]
 #![feature(cfg_target_feature)]
 #![feature(cfg_target_has_atomic)]
 #![feature(concat_idents)]

src/libcore/num/dec2flt/algorithm.rs

@@ -106,17 +106,17 @@ mod fpu_precision {
 /// a bignum.
 pub fn fast_path<T: RawFloat>(integral: &[u8], fractional: &[u8], e: i64) -> Option<T> {
     let num_digits = integral.len() + fractional.len();
-    // log_10(f64::max_sig) ~ 15.95. We compare the exact value to max_sig near the end,
+    // log_10(f64::MAX_SIG) ~ 15.95. We compare the exact value to MAX_SIG near the end,
     // this is just a quick, cheap rejection (and also frees the rest of the code from
     // worrying about underflow).
     if num_digits > 16 {
         return None;
     }
-    if e.abs() >= T::ceil_log5_of_max_sig() as i64 {
+    if e.abs() >= T::CEIL_LOG5_OF_MAX_SIG as i64 {
         return None;
     }
     let f = num::from_str_unchecked(integral.iter().chain(fractional.iter()));
-    if f > T::max_sig() {
+    if f > T::MAX_SIG {
         return None;
     }
 
@@ -154,14 +154,14 @@ pub fn fast_path<T: RawFloat>(integral: &[u8], fractional: &[u8], e: i64) -> Opt
 /// > the best possible approximation that uses p bits of significand.)
 pub fn bellerophon<T: RawFloat>(f: &Big, e: i16) -> T {
     let slop;
-    if f <= &Big::from_u64(T::max_sig()) {
+    if f <= &Big::from_u64(T::MAX_SIG) {
         // The cases abs(e) < log5(2^N) are in fast_path()
         slop = if e >= 0 { 0 } else { 3 };
     } else {
         slop = if e >= 0 { 1 } else { 4 };
     }
     let z = rawfp::big_to_fp(f).mul(&power_of_ten(e)).normalize();
-    let exp_p_n = 1 << (P - T::sig_bits() as u32);
+    let exp_p_n = 1 << (P - T::SIG_BITS as u32);
     let lowbits: i64 = (z.f % exp_p_n) as i64;
     // Is the slop large enough to make a difference when
     // rounding to n bits?
@@ -210,14 +210,14 @@ fn algorithm_r<T: RawFloat>(f: &Big, e: i16, z0: T) -> T {
         if d2 < y {
             let mut d2_double = d2;
             d2_double.mul_pow2(1);
-            if m == T::min_sig() && d_negative && d2_double > y {
+            if m == T::MIN_SIG && d_negative && d2_double > y {
                 z = prev_float(z);
             } else {
                 return z;
             }
         } else if d2 == y {
             if m % 2 == 0 {
-                if m == T::min_sig() && d_negative {
+                if m == T::MIN_SIG && d_negative {
                     z = prev_float(z);
                 } else {
                     return z;
@@ -303,12 +303,12 @@ pub fn algorithm_m<T: RawFloat>(f: &Big, e: i16) -> T {
     quick_start::<T>(&mut u, &mut v, &mut k);
     let mut rem = Big::from_small(0);
     let mut x = Big::from_small(0);
-    let min_sig = Big::from_u64(T::min_sig());
-    let max_sig = Big::from_u64(T::max_sig());
+    let min_sig = Big::from_u64(T::MIN_SIG);
+    let max_sig = Big::from_u64(T::MAX_SIG);
     loop {
         u.div_rem(&v, &mut x, &mut rem);
-        if k == T::min_exp_int() {
-            // We have to stop at the minimum exponent, if we wait until `k < T::min_exp_int()`,
+        if k == T::MIN_EXP_INT {
+            // We have to stop at the minimum exponent, if we wait until `k < T::MIN_EXP_INT`,
             // then we'd be off by a factor of two. Unfortunately this means we have to special-
             // case normal numbers with the minimum exponent.
             // FIXME find a more elegant formulation, but run the `tiny-pow10` test to make sure
@@ -318,8 +318,8 @@ pub fn algorithm_m<T: RawFloat>(f: &Big, e: i16) -> T {
             }
             return underflow(x, v, rem);
         }
-        if k > T::max_exp_int() {
-            return T::infinity2();
+        if k > T::MAX_EXP_INT {
+            return T::INFINITY;
         }
         if x < min_sig {
             u.mul_pow2(1);
@@ -345,18 +345,18 @@ fn quick_start<T: RawFloat>(u: &mut Big, v: &mut Big, k: &mut i16) {
     // The target ratio is one where u/v is in an in-range significand. Thus our termination
     // condition is log2(u / v) being the significand bits, plus/minus one.
     // FIXME Looking at the second bit could improve the estimate and avoid some more divisions.
-    let target_ratio = T::sig_bits() as i16;
+    let target_ratio = T::SIG_BITS as i16;
     let log2_u = u.bit_length() as i16;
     let log2_v = v.bit_length() as i16;
     let mut u_shift: i16 = 0;
     let mut v_shift: i16 = 0;
     assert!(*k == 0);
     loop {
-        if *k == T::min_exp_int() {
+        if *k == T::MIN_EXP_INT {
             // Underflow or subnormal. Leave it to the main function.
             break;
         }
-        if *k == T::max_exp_int() {
+        if *k == T::MAX_EXP_INT {
             // Overflow. Leave it to the main function.
             break;
         }
@@ -376,7 +376,7 @@ fn quick_start<T: RawFloat>(u: &mut Big, v: &mut Big, k: &mut i16) {
 }
 
 fn underflow<T: RawFloat>(x: Big, v: Big, rem: Big) -> T {
-    if x < Big::from_u64(T::min_sig()) {
+    if x < Big::from_u64(T::MIN_SIG) {
         let q = num::to_u64(&x);
         let z = rawfp::encode_subnormal(q);
         return round_by_remainder(v, rem, q, z);
@@ -395,9 +395,9 @@ fn underflow<T: RawFloat>(x: Big, v: Big, rem: Big) -> T {
     // needs to be rounded up. Only when the rounded off bits are 1/2 and the remainder
     // is zero, we have a half-to-even situation.
     let bits = x.bit_length();
-    let lsb = bits - T::sig_bits() as usize;
+    let lsb = bits - T::SIG_BITS as usize;
     let q = num::get_bits(&x, lsb, bits);
-    let k = T::min_exp_int() + lsb as i16;
+    let k = T::MIN_EXP_INT + lsb as i16;
     let z = rawfp::encode_normal(Unpacked::new(q, k));
     let q_even = q % 2 == 0;
     match num::compare_with_half_ulp(&x, lsb) {

src/libcore/num/dec2flt/mod.rs

@@ -214,11 +214,11 @@ fn dec2flt<T: RawFloat>(s: &str) -> Result<T, ParseFloatError> {
     let (sign, s) = extract_sign(s);
     let flt = match parse_decimal(s) {
         ParseResult::Valid(decimal) => convert(decimal)?,
-        ParseResult::ShortcutToInf => T::infinity2(),
-        ParseResult::ShortcutToZero => T::zero2(),
+        ParseResult::ShortcutToInf => T::INFINITY,
+        ParseResult::ShortcutToZero => T::ZERO,
         ParseResult::Invalid => match s {
-            "inf" => T::infinity2(),
-            "NaN" => T::nan2(),
+            "inf" => T::INFINITY,
+            "NaN" => T::NAN,
             _ => { return Err(pfe_invalid()); }
         }
     };
@@ -254,7 +254,7 @@ fn convert<T: RawFloat>(mut decimal: Decimal) -> Result<T, ParseFloatError> {
     // FIXME These bounds are rather conservative. A more careful analysis of the failure modes
     // of Bellerophon could allow using it in more cases for a massive speed up.
     let exponent_in_range = table::MIN_E <= e && e <= table::MAX_E;
-    let value_in_range = upper_bound <= T::max_normal_digits() as u64;
+    let value_in_range = upper_bound <= T::MAX_NORMAL_DIGITS as u64;
     if exponent_in_range && value_in_range {
         Ok(algorithm::bellerophon(&f, e))
     } else {
@@ -315,17 +315,17 @@ fn bound_intermediate_digits(decimal: &Decimal, e: i64) -> u64 {
 fn trivial_cases<T: RawFloat>(decimal: &Decimal) -> Option<T> {
     // There were zeros but they were stripped by simplify()
     if decimal.integral.is_empty() && decimal.fractional.is_empty() {
-        return Some(T::zero2());
+        return Some(T::ZERO);
     }
     // This is a crude approximation of ceil(log10(the real value)). We don't need to worry too
     // much about overflow here because the input length is tiny (at least compared to 2^64) and
     // the parser already handles exponents whose absolute value is greater than 10^18
     // (which is still 10^19 short of 2^64).
     let max_place = decimal.exp + decimal.integral.len() as i64;
-    if max_place > T::inf_cutoff() {
-        return Some(T::infinity2());
-    } else if max_place < T::zero_cutoff() {
-        return Some(T::zero2());
+    if max_place > T::INF_CUTOFF {
+        return Some(T::INFINITY);
+    } else if max_place < T::ZERO_CUTOFF {
+        return Some(T::ZERO);
     }
     None
 }

src/libcore/num/dec2flt/rawfp.rs

@@ -56,24 +56,12 @@ impl Unpacked {
 ///
 /// Should **never ever** be implemented for other types or be used outside the dec2flt module.
 /// Inherits from `Float` because there is some overlap, but all the reused methods are trivial.
-/// The "methods" (pseudo-constants) with default implementation should not be overriden.
 pub trait RawFloat : Float + Copy + Debug + LowerExp
                     + Mul<Output=Self> + Div<Output=Self> + Neg<Output=Self>
 {
-    // suffix of "2" because Float::infinity is deprecated
-    #[allow(deprecated)]
-    fn infinity2() -> Self {
-        Float::infinity()
-    }
-
-    // suffix of "2" because Float::nan is deprecated
-    #[allow(deprecated)]
-    fn nan2() -> Self {
-        Float::nan()
-    }
-
-    // suffix of "2" because Float::zero is deprecated
-    fn zero2() -> Self;
+    const INFINITY: Self;
+    const NAN: Self;
+    const ZERO: Self;
 
     // suffix of "2" because Float::integer_decode is deprecated
     #[allow(deprecated)]
@@ -94,94 +82,83 @@ pub trait RawFloat : Float + Copy + Debug + LowerExp
     /// represented, the other code in this module makes sure to never let that happen.
     fn from_int(x: u64) -> Self;
 
-    /// Get the value 10<sup>e</sup> from a pre-computed table. Panics for e >=
-    /// ceil_log5_of_max_sig().
+    /// Get the value 10<sup>e</sup> from a pre-computed table.
+    /// Panics for `e >= CEIL_LOG5_OF_MAX_SIG`.
     fn short_fast_pow10(e: usize) -> Self;
 
-    // FIXME Everything that follows should be associated constants, but taking the value of an
-    // associated constant from a type parameter does not work (yet?)
-    // A possible workaround is having a `FloatInfo` struct for all the constants, but so far
-    // the methods aren't painful enough to rewrite.
-
     /// What the name says. It's easier to hard code than juggling intrinsics and
     /// hoping LLVM constant folds it.
-    fn ceil_log5_of_max_sig() -> i16;
+    const CEIL_LOG5_OF_MAX_SIG: i16;
 
     // A conservative bound on the decimal digits of inputs that can't produce overflow or zero or
     /// subnormals. Probably the decimal exponent of the maximum normal value, hence the name.
-    fn max_normal_digits() -> usize;
+    const MAX_NORMAL_DIGITS: usize;
 
     /// When the most significant decimal digit has a place value greater than this, the number
     /// is certainly rounded to infinity.
-    fn inf_cutoff() -> i64;
+    const INF_CUTOFF: i64;
 
     /// When the most significant decimal digit has a place value less than this, the number
     /// is certainly rounded to zero.
-    fn zero_cutoff() -> i64;
+    const ZERO_CUTOFF: i64;
 
     /// The number of bits in the exponent.
-    fn exp_bits() -> u8;
+    const EXP_BITS: u8;
 
     /// The number of bits in the singificand, *including* the hidden bit.
-    fn sig_bits() -> u8;
+    const SIG_BITS: u8;
 
     /// The number of bits in the singificand, *excluding* the hidden bit.
-    fn explicit_sig_bits() -> u8 {
-        Self::sig_bits() - 1
-    }
+    const EXPLICIT_SIG_BITS: u8;
 
     /// The maximum legal exponent in fractional representation.
-    fn max_exp() -> i16 {
-        (1 << (Self::exp_bits() - 1)) - 1
-    }
+    const MAX_EXP: i16;
 
     /// The minimum legal exponent in fractional representation, excluding subnormals.
-    fn min_exp() -> i16 {
-        -Self::max_exp() + 1
-    }
+    const MIN_EXP: i16;
 
     /// `MAX_EXP` for integral representation, i.e., with the shift applied.
-    fn max_exp_int() -> i16 {
-        Self::max_exp() - (Self::sig_bits() as i16 - 1)
-    }
+    const MAX_EXP_INT: i16;
 
     /// `MAX_EXP` encoded (i.e., with offset bias)
-    fn max_encoded_exp() -> i16 {
-        (1 << Self::exp_bits()) - 1
-    }
+    const MAX_ENCODED_EXP: i16;
 
     /// `MIN_EXP` for integral representation, i.e., with the shift applied.
-    fn min_exp_int() -> i16 {
-        Self::min_exp() - (Self::sig_bits() as i16 - 1)
-    }
+    const MIN_EXP_INT: i16;
 
     /// The maximum normalized singificand in integral representation.
-    fn max_sig() -> u64 {
-        (1 << Self::sig_bits()) - 1
-    }
+    const MAX_SIG: u64;
 
     /// The minimal normalized significand in integral representation.
-    fn min_sig() -> u64 {
-        1 << (Self::sig_bits() - 1)
-    }
+    const MIN_SIG: u64;
 }
 
-impl RawFloat for f32 {
-    fn zero2() -> Self {
-        0.0
-    }
-
-    fn sig_bits() -> u8 {
-        24
-    }
-
-    fn exp_bits() -> u8 {
-        8
+// Mostly a workaround for #34344.
+macro_rules! other_constants {
+    ($type: ident) => {
+        const EXPLICIT_SIG_BITS: u8 = Self::SIG_BITS - 1;
+        const MAX_EXP: i16 = (1 << (Self::EXP_BITS - 1)) - 1;
+        const MIN_EXP: i16 = -Self::MAX_EXP + 1;
+        const MAX_EXP_INT: i16 = Self::MAX_EXP - (Self::SIG_BITS as i16 - 1);
+        const MAX_ENCODED_EXP: i16 = (1 << Self::EXP_BITS) - 1;
+        const MIN_EXP_INT: i16 = Self::MIN_EXP - (Self::SIG_BITS as i16 - 1);
+        const MAX_SIG: u64 = (1 << Self::SIG_BITS) - 1;
+        const MIN_SIG: u64 = 1 << (Self::SIG_BITS - 1);
+
+        const INFINITY: Self = $crate::$type::INFINITY;
+        const NAN: Self = $crate::$type::NAN;
+        const ZERO: Self = 0.0;
     }
+}
 
-    fn ceil_log5_of_max_sig() -> i16 {
-        11
-    }
+impl RawFloat for f32 {
+    const SIG_BITS: u8 = 24;
+    const EXP_BITS: u8 = 8;
+    const CEIL_LOG5_OF_MAX_SIG: i16 = 11;
+    const MAX_NORMAL_DIGITS: usize = 35;
+    const INF_CUTOFF: i64 = 40;
+    const ZERO_CUTOFF: i64 = -48;
+    other_constants!(f32);
 
     fn transmute(self) -> u64 {
         let bits: u32 = unsafe { transmute(self) };
@@ -207,37 +184,17 @@ impl RawFloat for f32 {
     fn short_fast_pow10(e: usize) -> Self {
         table::F32_SHORT_POWERS[e]
     }
-
-    fn max_normal_digits() -> usize {
-        35
-    }
-
-    fn inf_cutoff() -> i64 {
-        40
-    }
-
-    fn zero_cutoff() -> i64 {
-        -48
-    }
 }
 
 
 impl RawFloat for f64 {
-    fn zero2() -> Self {
-        0.0
-    }
-
-    fn sig_bits() -> u8 {
-        53
-    }
-
-    fn exp_bits() -> u8 {
-        11
-    }
-
-    fn ceil_log5_of_max_sig() -> i16 {
-        23
-    }
+    const SIG_BITS: u8 = 53;
+    const EXP_BITS: u8 = 11;
+    const CEIL_LOG5_OF_MAX_SIG: i16 = 23;
+    const MAX_NORMAL_DIGITS: usize = 305;
+    const INF_CUTOFF: i64 = 310;
+    const ZERO_CUTOFF: i64 = -326;
+    other_constants!(f64);
 
     fn transmute(self) -> u64 {
         let bits: u64 = unsafe { transmute(self) };
@@ -262,38 +219,27 @@ impl RawFloat for f64 {
     fn short_fast_pow10(e: usize) -> Self {
         table::F64_SHORT_POWERS[e]
     }
-
-    fn max_normal_digits() -> usize {
-        305
-    }
-
-    fn inf_cutoff() -> i64 {
-        310
-    }
-
-    fn zero_cutoff() -> i64 {
-        -326
-    }
-
 }
 
-/// Convert an Fp to the closest f64. Only handles number that fit into a normalized f64.
+/// Convert an Fp to the closest machine float type.
+/// Does not handle subnormal results.
 pub fn fp_to_float<T: RawFloat>(x: Fp) -> T {
     let x = x.normalize();
     // x.f is 64 bit, so x.e has a mantissa shift of 63
     let e = x.e + 63;
-    if e > T::max_exp() {
+    if e > T::MAX_EXP {
         panic!("fp_to_float: exponent {} too large", e)
-    }  else if e > T::min_exp() {
+    }  else if e > T::MIN_EXP {
         encode_normal(round_normal::<T>(x))
     } else {
         panic!("fp_to_float: exponent {} too small", e)
     }
 }
 
-/// Round the 64-bit significand to 53 bit with half-to-even. Does not handle exponent overflow.
+/// Round the 64-bit significand to T::SIG_BITS bits with half-to-even.
+/// Does not handle exponent overflow.
 pub fn round_normal<T: RawFloat>(x: Fp) -> Unpacked {
-    let excess = 64 - T::sig_bits() as i16;
+    let excess = 64 - T::SIG_BITS as i16;
     let half: u64 = 1 << (excess - 1);
     let (q, rem) = (x.f >> excess, x.f & ((1 << excess) - 1));
     assert_eq!(q << excess | rem, x.f);
@@ -303,8 +249,8 @@ pub fn round_normal<T: RawFloat>(x: Fp) -> Unpacked {
         Unpacked::new(q, k)
     } else if rem == half && (q % 2) == 0 {
         Unpacked::new(q, k)
-    } else if q == T::max_sig() {
-        Unpacked::new(T::min_sig(), k + 1)
+    } else if q == T::MAX_SIG {
+        Unpacked::new(T::MIN_SIG, k + 1)
     } else {
         Unpacked::new(q + 1, k)
     }
@@ -313,22 +259,22 @@ pub fn round_normal<T: RawFloat>(x: Fp) -> Unpacked {
 /// Inverse of `RawFloat::unpack()` for normalized numbers.
 /// Panics if the significand or exponent are not valid for normalized numbers.
 pub fn encode_normal<T: RawFloat>(x: Unpacked) -> T {
-    debug_assert!(T::min_sig() <= x.sig && x.sig <= T::max_sig(),
+    debug_assert!(T::MIN_SIG <= x.sig && x.sig <= T::MAX_SIG,
         "encode_normal: significand not normalized");
     // Remove the hidden bit
-    let sig_enc = x.sig & !(1 << T::explicit_sig_bits());
+    let sig_enc = x.sig & !(1 << T::EXPLICIT_SIG_BITS);
     // Adjust the exponent for exponent bias and mantissa shift
-    let k_enc = x.k + T::max_exp() + T::explicit_sig_bits() as i16;
-    debug_assert!(k_enc != 0 && k_enc < T::max_encoded_exp(),
+    let k_enc = x.k + T::MAX_EXP + T::EXPLICIT_SIG_BITS as i16;
+    debug_assert!(k_enc != 0 && k_enc < T::MAX_ENCODED_EXP,
         "encode_normal: exponent out of range");
     // Leave sign bit at 0 ("+"), our numbers are all positive
-    let bits = (k_enc as u64) << T::explicit_sig_bits() | sig_enc;
+    let bits = (k_enc as u64) << T::EXPLICIT_SIG_BITS | sig_enc;
     T::from_bits(bits)
 }
 
-/// Construct the subnormal. A mantissa of 0 is allowed and constructs zero.
+/// Construct a subnormal. A mantissa of 0 is allowed and constructs zero.
 pub fn encode_subnormal<T: RawFloat>(significand: u64) -> T {
-    assert!(significand < T::min_sig(), "encode_subnormal: not actually subnormal");
+    assert!(significand < T::MIN_SIG, "encode_subnormal: not actually subnormal");
     // Encoded exponent is 0, the sign bit is 0, so we just have to reinterpret the bits.
     T::from_bits(significand)
 }
@@ -364,8 +310,8 @@ pub fn prev_float<T: RawFloat>(x: T) -> T {
         Zero => panic!("prev_float: argument is zero"),
         Normal => {
             let Unpacked { sig, k } = x.unpack();
-            if sig == T::min_sig() {
-                encode_normal(Unpacked::new(T::max_sig(), k - 1))
+            if sig == T::MIN_SIG {
+                encode_normal(Unpacked::new(T::MAX_SIG, k - 1))
             } else {
                 encode_normal(Unpacked::new(sig - 1, k))
             }
@@ -380,7 +326,7 @@ pub fn prev_float<T: RawFloat>(x: T) -> T {
 pub fn next_float<T: RawFloat>(x: T) -> T {
     match x.classify() {
         Nan => panic!("next_float: argument is NaN"),
-        Infinite => T::infinity2(),
+        Infinite => T::INFINITY,
         // This seems too good to be true, but it works.
         // 0.0 is encoded as the all-zero word. Subnormals are 0x000m...m where m is the mantissa.
         // In particular, the smallest subnormal is 0x0...01 and the largest is 0x000F...F.