Merge pull request #28 from jlapeyre/fix-lambda

Define LAMBDA in only one place

Add comments referencing paper.

Closes #12

Author: jlapeyre

src/odgp.rs

@@ -4,17 +4,13 @@
 use crate::common::ib_to_bf_prec;
 use crate::math::{floorlog, pow_sqrt2, sqrt2};
 use crate::region::Interval;
+use crate::ring::z_root_two::LAMBDA;
 use crate::ring::{DRootTwo, ZRootTwo};
 use dashu_float::round::mode::HalfEven;
 use dashu_float::FBig;
 use dashu_int::IBig;
 use std::iter;
 
-const LAMBDA: ZRootTwo = ZRootTwo {
-    a: IBig::ONE,
-    b: IBig::ONE,
-};
-
 pub fn solve_odgp(i: Interval, j: Interval) -> impl Iterator<Item = ZRootTwo> {
     // Can't return two different iterator types. So we can't do this check.
     // I checked with dbg! to confirm that omitting this check is ok:

src/ring/mod.rs

@@ -4,7 +4,7 @@
 mod d_omega;
 mod d_root_two;
 mod z_omega;
-mod z_root_two;
+pub mod z_root_two;
 
 pub use d_omega::DOmega;
 pub use d_root_two::DRootTwo;

src/ring/z_root_two.rs

@@ -18,6 +18,15 @@ pub struct ZRootTwo {
     pub(crate) b: IBig,
 }
 
+// See Definition 3.5 on pg 3 of R+S for the definition of lambda (and delta)
+// Careful! There is a different, unrelated defintion of lambda in
+// the discussion in Definition 9.1 on page 19 of R+S. It is in fact
+// the fixed phase factor used in the up-to-phase algorithm.
+pub const LAMBDA: ZRootTwo = ZRootTwo {
+    a: IBig::ONE,
+    b: IBig::ONE,
+};
+
 impl ZRootTwo {
     pub fn new(a: IBig, b: IBig) -> Self {
         Self { a, b }

src/to_upright.rs

@@ -8,14 +8,11 @@ use crate::common::ib_to_bf_prec;
 use crate::grid_op::{EllipsePair, GridOp};
 use crate::math::{floorsqrt, log};
 use crate::region::{Ellipse, Rectangle};
-use crate::ring::{ZOmega, ZRootTwo};
+use crate::ring::z_root_two::LAMBDA;
+use crate::ring::ZOmega;
 use crate::tdgp::Region;
 use dashu_int::IBig;
 use num_traits::Pow;
-const LAMBDA: ZRootTwo = ZRootTwo {
-    a: IBig::ONE,
-    b: IBig::ONE,
-};
 
 fn reduction(
     ellipse_pair: EllipsePair,