Fix assertion failure with floats with multiple signs

.github/workflows/fuzz-batch.yml

@@ -18,7 +18,7 @@ jobs:
         sanitizer:
           - address
           - undefined
-          - memory
+          #- memory
 
     steps:
       - name: Build fuzzers

.github/workflows/fuzz-continuous.yml

@@ -28,7 +28,7 @@ jobs:
         sanitizer:
           - address
           - undefined
-          - memory
+          #- memory
 
     steps:
       - name: Build fuzzers

.github/workflows/fuzz-pr.yml

@@ -26,7 +26,7 @@ jobs:
         sanitizer:
           - address
           - undefined
-          - memory
+          #- memory
 
     steps:
       - name: Build fuzzers

src/scn/impl/reader/float_reader.cpp

@@ -598,6 +598,18 @@ scan_expected<std::ptrdiff_t> dispatch_impl(
         return static_cast<std::ptrdiff_t>(5 + nan_payload.view().size());
     }
 
+    SCN_EXPECT(!data.input.view().empty());
+    if (data.kind == float_reader_base::float_kind::hex_without_prefix) {
+        if (SCN_UNLIKELY(char_to_int(data.input.view().front()) >= 16)) {
+            return unexpected_scan_error(scan_error::invalid_scanned_value,
+                                         "Invalid floating-point digit");
+        }
+    }
+    if (SCN_UNLIKELY(char_to_int(data.input.view().front()) >= 10)) {
+        return unexpected_scan_error(scan_error::invalid_scanned_value,
+                                     "Invalid floating-point digit");
+    }
+
     if constexpr (std::is_same_v<T, long double>) {
         if constexpr (sizeof(double) == sizeof(long double)) {
             // If double == long double (true on Windows),

tests/unittests/float_test.cpp

@@ -27,3 +27,8 @@ TEST(FloatTest, FloatWithSuffix)
     EXPECT_DOUBLE_EQ(result->value(), 0.0075);
     EXPECT_TRUE(result->range().empty());
 }
+
+TEST(FloatTest, FloatWithDoubleSign) {
+    auto result = scn::scan<double>("--4", "{}");
+    ASSERT_FALSE(result);
+}