exactfloat: Remove OpenSSL dependency

CMakeLists.txt

@@ -60,7 +60,6 @@ add_definitions(-DABSL_MIN_LOG_LEVEL=1)
 if (NOT TARGET absl::base)
     find_package(absl REQUIRED)
 endif()
-find_package(OpenSSL REQUIRED)
 # pthreads isn't used directly, but this is still required for std::thread.
 find_package(Threads REQUIRED)
 
@@ -215,6 +214,7 @@ add_library(s2
             src/s2/util/bits/bit-interleave.cc
             src/s2/util/coding/coder.cc
             src/s2/util/coding/varint.cc
+            src/s2/util/math/exactfloat/bignum.cc
             src/s2/util/math/exactfloat/exactfloat.cc
             src/s2/util/math/mathutil.cc
             src/s2/util/units/length-units.cc)
@@ -230,7 +230,6 @@ endif()
 
 target_link_libraries(
     s2
-    ${OPENSSL_LIBRARIES}
     absl::absl_vlog_is_on
     absl::base
     absl::btree
@@ -459,7 +458,8 @@ if(S2_ENABLE_INSTALL)
                 src/s2/util/math/matrix3x3.h
                 src/s2/util/math/vector.h
           DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/s2/util/math")
-  install(FILES src/s2/util/math/exactfloat/exactfloat.h
+  install(FILES src/s2/util/math/exactfloat/bignum.h
+                src/s2/util/math/exactfloat/exactfloat.h
           DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/s2/util/math/exactfloat")
   install(FILES src/s2/util/units/length-units.h
                 src/s2/util/units/physical-units.h
@@ -489,6 +489,8 @@ if(S2_ENABLE_INSTALL)
 endif() # S2_ENABLE_INSTALL
 
 if (BUILD_TESTS)
+  find_package(OpenSSL REQUIRED)
+
   if (NOT GOOGLETEST_ROOT)
     message(FATAL_ERROR "BUILD_TESTS requires GOOGLETEST_ROOT")
   endif()
@@ -620,6 +622,7 @@ if (BUILD_TESTS)
       src/s2/s2wrapped_shape_test.cc
       src/s2/sequence_lexicon_test.cc
       src/s2/value_lexicon_test.cc
+      src/s2/util/math/exactfloat/bignum_test.cc
       src/s2/util/math/exactfloat/exactfloat_test.cc
       src/s2/util/math/exactfloat/exactfloat_underflow_test.cc)
 
@@ -630,6 +633,7 @@ if (BUILD_TESTS)
     add_executable(${test} ${test_cc})
     target_link_libraries(
         ${test}
+        ${OPENSSL_CRYPTO_LIBRARIES}
         s2testing s2
         absl::base
         absl::btree

README.md

@@ -59,7 +59,6 @@ This issue may require revision of boringssl or exactfloat.
 *   [Abseil](https://github.com/abseil/abseil-cpp) LTS
     [`20250814`](https://github.com/abseil/abseil-cpp/releases/tag/20250814.1)
     (standard library extensions). This exact version must be used.
-*   [OpenSSL](https://github.com/openssl/openssl) (for its bignum library)
 *   [googletest testing framework >= 1.10](https://github.com/google/googletest)
     (to build tests and example programs, optional)
 
@@ -139,6 +138,13 @@ Disable building of shared libraries with `-DBUILD_SHARED_LIBS=OFF`.
 
 Enable the python interface with `-DWITH_PYTHON=ON`.
 
+# For Testing
+
+If BUILD_TESTS is 'on' (the default), then OpenSSL must be available to build
+some tests:
+
+*   [OpenSSL](https://github.com/openssl/openssl) (for its bignum library)
+
 If OpenSSL is installed in a non-standard location set `OPENSSL_ROOT_DIR`
 before running configure, for example on macOS:
 ```
@@ -218,7 +224,7 @@ python -m build
 
 The resulting wheel will be in the `dist` directory.
 
-> If OpenSSL is in a non-standard location make sure to set `OPENSSL_ROOT_DIR`; 
+> If OpenSSL is in a non-standard location make sure to set `OPENSSL_ROOT_DIR`;
 > see above for more information.
 
 ## Other S2 implementations

src/s2/util/math/exactfloat/BUILD

@@ -1,14 +1,37 @@
 package(default_visibility = ["//visibility:public"])
 
+cc_library(
+    name = "bignum",
+    srcs = ["bignum.cc"],
+    hdrs = ["bignum.h"],
+    visibility = ["//visibility:private"],
+    deps = [
+        "@abseil-cpp//absl/algorithm:container",
+        "@abseil-cpp//absl/container:inlined_vector",
+        "@abseil-cpp//absl/log:absl_check",
+    ],
+)
+
 cc_library(
     name = "exactfloat",
     srcs = ["exactfloat.cc"],
     hdrs = ["exactfloat.h"],
     deps = [
+        ":bignum",
         "//s2/base:logging",
-        "@abseil-cpp//absl/log:log",
-        "@abseil-cpp//absl/log:absl_check",
+    ],
+)
+
+cc_test(
+    name = "bignum_test",
+    srcs = ["bignum_test.cc"],
+    deps = [
+        ":bignum",
+        "//:s2_testing_headers",
+        "@abseil-cpp//absl/log:log_streamer",
+        "@abseil-cpp//absl/random:bit_gen_ref",
         "@boringssl//:crypto",
+        "@googletest//:gtest_main",
     ],
 )
 
@@ -30,6 +53,7 @@ cc_test(
     srcs = ["exactfloat_underflow_test.cc"],
     deps = [
         ":exactfloat",
+        "@abseil-cpp//absl/random:random",
         "@googletest//:gtest_main",
     ],
 )