Module core::num::dec2flt::rawfp
[−]
[src]
dec2flt
): internal routines only exposed for testing
Bit fiddling on positive IEEE 754 floats. Negative numbers aren't and needn't be handled. Normal floating point numbers have a canonical representation as (frac, exp) such that the value is 2^{exp} * (1 + sum(frac[N-i] / 2^{i))} where N is the number of bits. Subnormals are slightly different and weird, but the same principle applies.
Here, however, we represent them as (sig, k) with f positive, such that the value is f * 2^{e.} Besides making the "hidden bit" explicit, this changes the exponent by the so-called mantissa shift.
Put another way, normally floats are written as (1) but here they are written as (2):
1.101100...11 * 2^m
1101100...11 * 2^n
We call (1) the fractional representation and (2) the integral representation.
Many functions in this module only handle normal numbers. The dec2flt routines conservatively take the universally-correct slow path (Algorithm M) for very small and very large numbers. That algorithm needs only next_float() which does handle subnormals and zeros.
Reexports
use prelude::v1::*; |
use u32; |
use cmp::Ordering::{Less, Equal, Greater}; |
use ops::{Mul, Div, Neg}; |
use fmt::{Debug, LowerExp}; |
use mem::transmute; |
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; |
Structs
Unpacked | [Unstable] |
Traits
RawFloat |
[Unstable] A helper trait to avoid duplicating basically all the conversion code for |
Functions
big_to_fp |
[Unstable] Approximate a bignum with an Fp. Rounds within 0.5 ULP with half-to-even. |
encode_normal |
[Unstable] Inverse of |
encode_subnormal |
[Unstable] Construct the subnormal. A mantissa of 0 is allowed and constructs zero. |
fp_to_float |
[Unstable] Convert an Fp to the closest f64. Only handles number that fit into a normalized f64. |
next_float | [Unstable] |
prev_float |
[Unstable] Find the largest floating point number strictly smaller than the argument. Does not handle subnormals, zero, or exponent underflow. |
round_normal |
[Unstable] Round the 64-bit significand to 53 bit with half-to-even. Does not handle exponent overflow. |