diff options
| -rw-r--r-- | src/etc/dec2flt_table.py | 35 | ||||
| -rw-r--r-- | src/libcore/num/dec2flt/algorithm.rs | 10 | ||||
| -rw-r--r-- | src/libcore/num/dec2flt/rawfp.rs | 12 | ||||
| -rw-r--r-- | src/libcore/num/dec2flt/table.rs | 46 |
4 files changed, 88 insertions, 15 deletions
diff --git a/src/etc/dec2flt_table.py b/src/etc/dec2flt_table.py index b0140fb2455..9fdab1fcfca 100644 --- a/src/etc/dec2flt_table.py +++ b/src/etc/dec2flt_table.py @@ -25,6 +25,7 @@ even larger, and it's already uncomfortably large (6 KiB). """ from __future__ import print_function import sys +from math import ceil, log from fractions import Fraction from collections import namedtuple @@ -33,7 +34,6 @@ N = 64 # Size of the significand field in bits MIN_SIG = 2 ** (N - 1) MAX_SIG = (2 ** N) - 1 - # Hand-rolled fp representation without arithmetic or any other operations. # The significand is normalized and always N bit, but the exponent is # unrestricted in range. @@ -92,7 +92,7 @@ def error(f, e, z): ulp_err = abs_err / Fraction(2) ** z.exp return float(ulp_err) -LICENSE = """ +HEADER = """ // Copyright 2015 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. @@ -102,9 +102,23 @@ LICENSE = """ // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. + +//! Tables of approximations of powers of ten. +//! DO NOT MODIFY: Generated by `src/etc/dec2flt_table.py` """ + def main(): + print(HEADER.strip()) + print() + print_proper_powers() + print() + print_short_powers(32, 24) + print() + print_short_powers(64, 53) + + +def print_proper_powers(): MIN_E = -305 MAX_E = 305 e_range = range(MIN_E, MAX_E+1) @@ -114,13 +128,10 @@ def main(): err = error(1, e, z) assert err < 0.5 powers.append(z) - typ = "([u64; {0}], [i16; {0}])".format(len(e_range)) - print(LICENSE.strip()) - print("// Table of approximations of powers of ten.") - print("// DO NOT MODIFY: Generated by a src/etc/dec2flt_table.py") print("pub const MIN_E: i16 = {};".format(MIN_E)) print("pub const MAX_E: i16 = {};".format(MAX_E)) print() + typ = "([u64; {0}], [i16; {0}])".format(len(powers)) print("pub const POWERS: ", typ, " = ([", sep='') for z in powers: print(" 0x{:x},".format(z.sig)) @@ -130,5 +141,17 @@ def main(): print("]);") +def print_short_powers(num_bits, significand_size): + max_sig = 2**significand_size - 1 + # The fast path bails out for exponents >= ceil(log5(max_sig)) + max_e = int(ceil(log(max_sig, 5))) + e_range = range(max_e) + typ = "[f{}; {}]".format(num_bits, len(e_range)) + print("pub const F", num_bits, "_SHORT_POWERS: ", typ, " = [", sep='') + for e in e_range: + print(" 1e{},".format(e)) + print("];") + + if __name__ == '__main__': main() diff --git a/src/libcore/num/dec2flt/algorithm.rs b/src/libcore/num/dec2flt/algorithm.rs index 1f0f06d7461..82d3389edc4 100644 --- a/src/libcore/num/dec2flt/algorithm.rs +++ b/src/libcore/num/dec2flt/algorithm.rs @@ -60,17 +60,13 @@ pub fn fast_path<T: RawFloat>(integral: &[u8], fractional: &[u8], e: i64) -> Opt if f > T::max_sig() { return None; } - let e = e as i16; // Can't overflow because e.abs() <= LOG5_OF_EXP_N // The case e < 0 cannot be folded into the other branch. Negative powers result in // a repeating fractional part in binary, which are rounded, which causes real // (and occasioally quite significant!) errors in the final result. - // The case `e == 0`, however, is unnecessary for correctness. It's just measurably faster. - if e == 0 { - Some(T::from_int(f)) - } else if e > 0 { - Some(T::from_int(f) * fp_to_float(power_of_ten(e))) + if e >= 0 { + Some(T::from_int(f) * T::short_fast_pow10(e as usize)) } else { - Some(T::from_int(f) / fp_to_float(power_of_ten(-e))) + Some(T::from_int(f) / T::short_fast_pow10(e.abs() as usize)) } } diff --git a/src/libcore/num/dec2flt/rawfp.rs b/src/libcore/num/dec2flt/rawfp.rs index 19758974003..2099c6a7baa 100644 --- a/src/libcore/num/dec2flt/rawfp.rs +++ b/src/libcore/num/dec2flt/rawfp.rs @@ -37,6 +37,7 @@ use num::diy_float::Fp; use num::FpCategory::{Infinite, Zero, Subnormal, Normal, Nan}; use num::Float; use num::dec2flt::num::{self, Big}; +use num::dec2flt::table; #[derive(Copy, Clone, Debug)] pub struct Unpacked { @@ -73,6 +74,9 @@ 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^e 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 @@ -175,6 +179,10 @@ impl RawFloat for f32 { x as f32 } + fn short_fast_pow10(e: usize) -> Self { + table::F32_SHORT_POWERS[e] + } + fn max_normal_digits() -> usize { 35 } @@ -222,6 +230,10 @@ impl RawFloat for f64 { x as f64 } + fn short_fast_pow10(e: usize) -> Self { + table::F64_SHORT_POWERS[e] + } + fn max_normal_digits() -> usize { 305 } diff --git a/src/libcore/num/dec2flt/table.rs b/src/libcore/num/dec2flt/table.rs index dd985fd155b..cb8c94313d0 100644 --- a/src/libcore/num/dec2flt/table.rs +++ b/src/libcore/num/dec2flt/table.rs @@ -7,8 +7,10 @@ // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. -// Table of approximations of powers of ten. -// DO NOT MODIFY: Generated by a src/etc/dec2flt_table.py + +//! Tables of approximations of powers of ten. +//! DO NOT MODIFY: Generated by `src/etc/dec2flt_table.py` + pub const MIN_E: i16 = -305; pub const MAX_E: i16 = 305; @@ -1237,3 +1239,43 @@ pub const POWERS: ([u64; 611], [i16; 611]) = ([ 946, 950, ]); + +pub const F32_SHORT_POWERS: [f32; 11] = [ + 1e0, + 1e1, + 1e2, + 1e3, + 1e4, + 1e5, + 1e6, + 1e7, + 1e8, + 1e9, + 1e10, +]; + +pub const F64_SHORT_POWERS: [f64; 23] = [ + 1e0, + 1e1, + 1e2, + 1e3, + 1e4, + 1e5, + 1e6, + 1e7, + 1e8, + 1e9, + 1e10, + 1e11, + 1e12, + 1e13, + 1e14, + 1e15, + 1e16, + 1e17, + 1e18, + 1e19, + 1e20, + 1e21, + 1e22, +]; |