From ec172e1745c640f01c42d1e81b14f4c2ea69acd4 Mon Sep 17 00:00:00 2001
From: David Byers <david.byers@liu.se>
Date: Tue, 21 Jul 2020 21:17:23 +0200
Subject: [PATCH] Rewrote olc-decode to use integer math.
---
CHANGELOG | 3 +++
olc.el | 35 ++++++++++++++++++++++-------------
test/olctest.el | 7 ++++---
3 files changed, 29 insertions(+), 16 deletions(-)
diff --git a/CHANGELOG b/CHANGELOG
index deef8f4..9caef53 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,5 +1,8 @@
2020-07-21 David Byers <david.byers@liu.se>
+ More integer math:
+ (olc-decode): Converted to use integer math.
+
Wrote texinfo documentation:
* olc.el (olc-parse-length): Removed.
Updated documentation comment.
diff --git a/olc.el b/olc.el
index 64715dc..1b7273b 100644
--- a/olc.el
+++ b/olc.el
@@ -264,10 +264,13 @@ coordinates, an empty code, and so forth).
Since this function uses floating point calculations, the results
are not identical to e.g. the C++ reference implementation. The
differences, however, are extremely small."
- (let ((parse (olc-parse-code code))
- (lat -90.0)
- (lon -180.0)
- (size 20.0))
+ (let* ((parse (olc-parse-code code))
+ (latscale (* (expt 20 4) (expt 5 5)))
+ (lonscale (* (expt 20 4) (expt 4 5)))
+ (lat (* latscale -90))
+ (lon (* lonscale -180))
+ (latsize (* latscale 20))
+ (lonsize (* lonscale 20)))
;; We only deal with long codes
(when (olc-parse-short parse)
@@ -275,22 +278,28 @@ differences, however, are extremely small."
;; Process the pairs
(mapc (lambda (pair)
- (setq lat (+ lat (* size (olc-digit-value (car pair))))
- lon (+ lon (* size (olc-digit-value (cdr pair))))
- width size
- height size
- size (/ size 20.0)))
+ (setq lat (+ lat (* latsize (olc-digit-value (car pair))))
+ lon (+ lon (* lonsize (olc-digit-value (cdr pair))))
+ latsize (/ latsize 20)
+ lonsize (/ lonsize 20)))
(olc-parse-pairs parse))
+ ;; I'm too tired to figure out why
+ (setq latsize (* latsize 20) lonsize (* lonsize 20))
+
;; Process the grid
(when (olc-parse-grid parse)
(mapc (lambda (refine)
- (setq width (/ width 4.0) height (/ height 5.0))
+ (setq latsize (/ latsize 5) lonsize (/ lonsize 4))
(let ((coord (olc-digit-value refine)))
- (setq lat (+ lat (* height (/ coord 4)))
- lon (+ lon (* width (% coord 4))))))
+ (setq lat (+ lat (* latsize (/ coord 4)))
+ lon (+ lon (* lonsize (% coord 4))))))
(olc-parse-grid parse)))
- (olc-area-create :latlo lat :lonlo lon :lathi (+ lat height) :lonhi (+ lon width))))
+
+ (olc-area-create :latlo (/ lat (float latscale))
+ :lonlo (/ lon (float lonscale))
+ :lathi (/ (+ lat latsize) (float latscale))
+ :lonhi (/ (+ lon lonsize) (float lonscale)))))
(defun olc-encode (lat lon len)
diff --git a/test/olctest.el b/test/olctest.el
index bf2af42..e042345 100644
--- a/test/olctest.el
+++ b/test/olctest.el
@@ -18,8 +18,9 @@
(require 'cl-lib)
-;; Decode still uses float arithmetic, so results can be slightly off
-;; from the test cases. This is deemed acceptable.
+;; Due to rounding and floating point representation we can't seem
+;; to get closer than 1e-10 to the reference test cases, but sinze
+;; it only affects decoding, that is an insignificant error level.
(defvar olctest-decode-tolerance 0.0000000001)
@@ -196,7 +197,7 @@
(defun olctest-run-all ()
"Run all tests."
- (and (olctest-decode)
+ (and (olctest-decode)q
(olctest-encode)
(olctest-shortcodes)
(olctest-validity)
--
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