Fix WKTWriter for small precisions and with trim enabled (#1199)

NEWS.md

@@ -9,6 +9,7 @@
   - Fix ConcaveHullOfPolygons nested shell handling (GH-1169, Martin Davis)
   - Fix RelateNG for computing IM for empty-nonempty cases (Martin Davis)
   - Fix TopologyPreservingSimplifier/TaggedLineString to avoid jumping components (JTS-1096, Martin Davis)
+  - Fix WKTWriter for small precisions and with trim enabled (GH-1199, Mike Taves)
 
 ## Changes in 3.13.0
 2024-09-06

src/io/WKTWriter.cpp

@@ -460,7 +460,10 @@ WKTWriter::writeTrimmedNumber(double d, uint32_t precision, char* buf)
         // most real-world coordinates, use positional notation
         if ( (precision < 4) && (da < 1.0) ) {
             // adjust precision to avoid rounding to zero
-            precision = static_cast<std::uint32_t>(-floor(log10(da)));
+            const auto higher_prec = static_cast<std::uint32_t>(-floor(log10(da)));
+            if (higher_prec > precision) {
+                precision = higher_prec;
+            }
         }
         return geos_d2sfixed_buffered_n(d, precision, buf);
     }

tests/unit/capi/GEOS_printDoubleTest.cpp

@@ -69,6 +69,21 @@ void object::test<1>()
         TESTCASE(12, 1.2345678901234e+17, "1.234567890123e+17"),
         TESTCASE(13, 1.2345678901234e+17, "1.2345678901234e+17"),
         TESTCASE(14, 1.2345678901234e+17, "1.2345678901234e+17"),
+        TESTCASE(0, 0.0123456789, "0.01"),
+        TESTCASE(1, 0.0123456789, "0.01"),
+        TESTCASE(2, 0.0123456789, "0.01"),
+        TESTCASE(3, 0.0123456789, "0.012"),
+        TESTCASE(4, 0.0123456789, "0.0123"),
+        TESTCASE(0, 0.123456789, "0.1"),
+        TESTCASE(1, 0.123456789, "0.1"),
+        TESTCASE(2, 0.123456789, "0.12"),
+        TESTCASE(3, 0.123456789, "0.123"),
+        TESTCASE(4, 0.123456789, "0.1235"),
+        TESTCASE(0, 1.23456789, "1"),
+        TESTCASE(1, 1.23456789, "1.2"),
+        TESTCASE(2, 1.23456789, "1.23"),
+        TESTCASE(3, 1.23456789, "1.235"),
+        TESTCASE(4, 1.23456789, "1.2346"),
     };
     for (const auto& testcase : testcase_l) {
         char buf[28];