Squashed commit of the following:

commit ab1b004
Author: Paul Ramsey <[email protected]>
Date:   Thu Apr 16 14:40:23 2020 -0700

    remove ttmath in favour of DD

commit 472c1f9
Merge: 8ccf3bf 312c085
Author: Paul Ramsey <[email protected]>
Date:   Thu Apr 16 13:24:39 2020 -0700

    Merge branch 'master' of https://git.osgeo.org/gitea/geos/geos into master-dd

commit 8ccf3bf
Author: Paul Ramsey <[email protected]>
Date:   Thu Apr 16 13:10:25 2020 -0700

    add informational comment

commit 8fd12e0
Author: Paul Ramsey <[email protected]>
Date:   Thu Apr 16 12:15:00 2020 -0700

    add in all JTS unit tests for doubledouble calculations

commit e24af3b
Author: Paul Ramsey <[email protected]>
Date:   Wed Apr 15 13:47:56 2020 -0700

    autotools build

commit cb5942a
Author: Paul Ramsey <[email protected]>
Date:   Wed Apr 15 13:31:28 2020 -0700

    fix doxygen complaint?

commit 469037a
Author: Paul Ramsey <[email protected]>
Date:   Wed Apr 15 12:47:14 2020 -0700

    change name of ifdef guard

commit 00559ec
Author: Paul Ramsey <[email protected]>
Date:   Wed Apr 15 12:40:50 2020 -0700

    allow DD to swap in for ttmath

commit 75e70f7
Author: Paul Ramsey <[email protected]>
Date:   Wed Apr 15 11:28:15 2020 -0700

    clean build of all DD functionality from JTS

commit e42e9bc
Author: Paul Ramsey <[email protected]>
Date:   Tue Apr 14 17:27:45 2020 -0700

    DD wip

.codecov.yml

@@ -2,7 +2,6 @@ coverage:
   precision: 2
 
 ignore:
-  - "include/geos/algorithm/ttmath"
   - "tests/unit/tut"
   - "tests/xmltester/tinyxml2"
 

Makefile.am

@@ -73,5 +73,4 @@ valgrindcheck:
 check-local:
 	! find $(srcdir) -name '*.cpp' -o -name '*.h' | \
 		grep -v tests/xmltester/tinyxml | \
-		grep -v include/geos/algorithm/ttmath | \
 		xargs grep -n '[[:space:]]$$'

configure.ac

@@ -376,7 +376,6 @@ AC_OUTPUT([
 	include/geos/algorithm/Makefile
 	include/geos/algorithm/locate/Makefile
 	include/geos/algorithm/distance/Makefile
-	include/geos/algorithm/ttmath/Makefile
 	include/geos/geom/Makefile
 	include/geos/geom/prep/Makefile
 	include/geos/geom/util/Makefile
@@ -391,6 +390,7 @@ AC_OUTPUT([
 	include/geos/index/sweepline/Makefile
 	include/geos/io/Makefile
 	include/geos/linearref/Makefile
+	include/geos/math/Makefile
 	include/geos/noding/Makefile
 	include/geos/noding/snapround/Makefile
 	include/geos/operation/Makefile
@@ -423,6 +423,7 @@ AC_OUTPUT([
 	src/index/sweepline/Makefile
 	src/io/Makefile
 	src/linearref/Makefile
+	src/math/Makefile
 	src/noding/Makefile
 	src/noding/snapround/Makefile
 	src/operation/Makefile

doc/Doxyfile.in

@@ -853,7 +853,6 @@ EXCLUDE_PATTERNS       = */examples/* \
                          */test/* \
                          */bigtest/* \
                          */io/markup/* \
-                         */ttmath/* \
                          config.h \
                          acconfig.h \
                          CoordinateList.cpp \

include/geos/Makefile.am

@@ -8,6 +8,7 @@ SUBDIRS = \
     index \
     io \
     linearref \
+    math \
     noding \
     operation \
     planargraph \

include/geos/algorithm/CGAlgorithmsDD.h

@@ -19,17 +19,7 @@
 #ifndef GEOS_ALGORITHM_CGALGORITHMDD_H
 #define GEOS_ALGORITHM_CGALGORITHMDD_H
 #include <geos/export.h>
-#include <geos/algorithm/ttmath/ttmath.h>
-
-/// \file CGAlgorithmsDD.h
-
-/// \brief Close to DoubleDouble equivalent used by JTS
-///
-/// Usage: `ttmath::Big<exponent, mantissa>`
-typedef ttmath::Big<TTMATH_BITS(32), TTMATH_BITS(128)> DD;
-//typedef ttmath::Big<TTMATH_BITS(64), TTMATH_BITS(128)> DD;
-//typedef ttmath::Big<TTMATH_BITS(32), TTMATH_BITS(256)> DD;
-//typedef ttmath::Big<TTMATH_BITS(64), TTMATH_BITS(256)> DD;
+#include <geos/math/DD.h>
 
 // Forward declarations
 namespace geos {
@@ -39,6 +29,8 @@ class CoordinateSequence;
 }
 }
 
+using namespace geos::math;
+
 namespace geos {
 namespace algorithm { // geos::algorithm
 
@@ -139,7 +131,7 @@ class GEOS_DLL CGAlgorithmsDD {
      * The circumcentre does not necessarily lie within the triangle. For example,
      * the circumcentre of an obtuse isosceles triangle lies outside the triangle.
      *
-     * This method uses @ref DD extended-precision arithmetic to provide more accurate
+     * This method uses @ref geos::math::DD extended-precision arithmetic to provide more accurate
      * results than [circumcentre(Coordinate, Coordinate, Coordinate)]
      * (@ref geos::geom::Triangle::circumcentre(const Coordinate& p0, const Coordinate& p1, const Coordinate& p2)).
      *

include/geos/algorithm/Makefile.am

@@ -3,8 +3,7 @@
 #
 SUBDIRS = \
 	locate \
-	distance \
-	ttmath
+	distance 
 
 EXTRA_DIST =
 

include/geos/algorithm/RayCrossingCounterDD.h

@@ -22,7 +22,6 @@
 
 #include <geos/export.h>
 #include <geos/geom/Location.h>
-#include <geos/algorithm/ttmath/ttmath.h>
 
 #include <vector>