Precise parsing of floats (#4)

* Precise parsing of floats * Updated version
Nitrillo · Oct 18, 2022 · 2be2a1d · 2be2a1d
1 parent 40d9b7e
commit 2be2a1d
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Showing 3 changed files with 61 additions and 6 deletions.
diff --git a/examples/function.cpp b/examples/function.cpp
@@ -30,7 +30,9 @@ auto main() -> int {
         std::cout << result.getError() << std::endl;
     }
 
-    pm.addFunction("rand", [](picomath::number_t input) -> picomath::number_t { return input * rand() / RAND_MAX; });
+    pm.addFunction("rand", [](picomath::number_t input) -> picomath::number_t {
+        return input * static_cast<picomath::number_t>(rand()) / static_cast<picomath::number_t>(RAND_MAX);
+    });
     result = pm.evalExpression("rand(100)");
     if (result.isOk()) {
         std::cout << "Result: " << result.getResult() << std::endl;

diff --git a/include/picomath.hpp b/include/picomath.hpp
@@ -2,7 +2,7 @@
  * @file picomath.hpp
  * @author Cesar Guirao Robles (a.k.a. Nitro) <cesar@no2.es>
  * @brief Math expression evaluation. BSD 3-Clause License
- * @version 1.0.0
+ * @version 1.1.0
  * @date 2022-06-01
  *
  * @copyright Copyright (c) 2022, Cesar Guirao Robles (a.k.a. Nitro) <cesar@no2.es>
@@ -21,6 +21,12 @@
 
 namespace picomath {
 
+// Enable to use correct and precise float parsing
+// #define PM_USE_PRECISE_FLOAT_PARSING
+
+// Enable to use floats instead of doubles
+// #define PM_USE_FLOAT
+
 #ifndef PM_MAX_ARGUMENTS
 #define PM_MAX_ARGUMENTS 8
 #endif
@@ -35,8 +41,14 @@ class PicoMath;
 
 #ifdef PM_USE_FLOAT
 using number_t = float;
+#ifdef PM_USE_PRECISE_FLOAT_PARSING
+#define PM_STR_TO_FLOAT strtof
+#endif
 #else
 using number_t = double;
+#ifdef PM_USE_PRECISE_FLOAT_PARSING
+#define PM_STR_TO_FLOAT strtod
+#endif
 #endif
 using argument_list_t        = std::array<number_t, PM_MAX_ARGUMENTS>;
 using error_t                = std::string;
@@ -305,6 +317,18 @@ class Expression {
         return *str == 0;
     }
 
+    [[nodiscard]] PM_INLINE auto isSign() const -> bool {
+        return *str == '+' || *str == '-';
+    }
+
+    [[nodiscard]] PM_INLINE auto isExponent() const -> bool {
+        // This doesn't read out of bounds because:
+        // if first character is 'e' or 'E', next character can be a valid character
+        // or zero if it's the end of the string
+        return (*str == 'e' || *str == 'E') &&
+               (*(str + 1) == '+' || *(str + 1) == '-' || (*(str + 1) >= '0' && *(str + 1) <= '9'));
+    }
+
     PM_INLINE auto parseFunction(std::string_view identifier) noexcept -> Result {
         auto f = context.functions.find(identifier);
         if (PM_UNLIKELY(f == context.functions.end())) {
@@ -409,9 +433,17 @@ class Expression {
     PM_INLINE auto parseNumber() noexcept -> Result {
         number_t ret = 0;
 
-        while (isDigit()) {
-            ret *= 10;
-            ret += *str - '0';
+#if defined(PM_USE_PRECISE_FLOAT_PARSING)
+        char *end;
+        ret = PM_STR_TO_FLOAT(str, &end);
+        if (PM_UNLIKELY(errno == ERANGE)) {
+            std::string_view identifier{str, static_cast<size_t>(end - str)};
+            return generateError("Float out of range", identifier);
+        }
+        str = end;
+#else
+        while (PM_LIKELY(isDigit())) {
+            ret = ret * 10 + (*str - '0');
             consume();
         }
         // Decimal point
@@ -424,7 +456,22 @@ class Expression {
                 consume();
             }
         }
-
+        if (PM_UNLIKELY(isExponent())) {
+            consume();
+            bool sign = false;
+            if (isSign()) {
+                if (consume() == '-') {
+                    sign = true;
+                }
+            }
+            int exp = 0;
+            while (PM_LIKELY(isDigit())) {
+                exp = exp * 10 + (*str - '0');
+                consume();
+            }
+            ret *= std::pow(static_cast<number_t>(10), sign ? -exp : exp);
+        }
+#endif
         // Space before units
         consumeSpace();
 

diff --git a/test/test.cpp b/test/test.cpp
@@ -21,6 +21,9 @@ TEST_CASE("Simple expressions") {
     REQUIRE(AreSame(ctx.evalExpression("2.003 * 1000").getResult(), 2003.0));
     REQUIRE(AreSame(ctx.evalExpression(".1234").getResult(), 0.1234));
     REQUIRE(AreSame(ctx.evalExpression("123.1234").getResult(), 123.1234));
+    REQUIRE(AreSame(ctx.evalExpression("5e+7").getResult(), 50000000.0));
+    REQUIRE(AreSame(ctx.evalExpression("5e7").getResult(), 50000000.0));
+    REQUIRE(AreSame(ctx.evalExpression("5.0E-7").getResult(), 0.00000049999999873762));
     REQUIRE(AreSame(ctx.evalExpression("-(2+2)").getResult(), -4));
     REQUIRE(ctx.evalExpression("(2+2)").isOk());
     REQUIRE_FALSE(ctx.evalExpression("(2+2)").isError());
@@ -62,6 +65,9 @@ TEST_CASE("Custom units") {
     REQUIRE(AreSame(ctx.evalExpression("1km").getResult(), 1000.0));
     REQUIRE(AreSame(ctx.evalExpression("100km").getResult(), 100000.0));
     REQUIRE(AreSame(ctx.evalExpression("100km - 10").getResult(), 100000.0 - 10.0));
+
+    ctx.addUnit("em") = 10.0;
+    REQUIRE(AreSame(ctx.evalExpression("1em").getResult(), 10.0));
 }
 
 TEST_CASE("Invalid expressions") {