libc: Add borrowed strtod implementation

libc/CMakeLists.txt

@@ -24,6 +24,7 @@ set(SOURCES
     src/signal.cpp
     src/termios.cpp
     src/utime.cpp
+    src/strtod.cpp
     src/sys/stat.cpp
     src/sys/mman.cpp
     src/sys/wait.cpp

libc/include/stdlib.h

@@ -84,9 +84,11 @@ extern "C"
     /* Parse a decimal integer from a string. */
     long long atoll(const char* s);
 
-    double atof(const char*);
+    /* Parse a floating-point number from a string. */
+    double atof(const char* str);
 
-    double strtod(const char*, char**);
+    /* Parse a floating-point number from a string. */
+    double strtod(const char* str, char** endptr);
 
     /* Parse an integer of the specified base from a string, storing the first non-number character in endptr if
      * nonnull. */

libc/src/stdlib.cpp

@@ -297,4 +297,9 @@ extern "C"
             if (errno != EEXIST) return -1;
         }
     }
+
+    double atof(const char* str)
+    {
+        return strtod(str, nullptr);
+    }
 }

libc/src/strtod.cpp

@@ -0,0 +1,141 @@
+/* vi:set ts=8 sts=4 sw=4: */
+/*
+ * strtod implementation.
+ * author: Yasuhiro Matsumoto
+ * license: public domain
+ *
+ * source from https://gist.github.com/mattn/1890186
+ */
+
+#include <ctype.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static const char* skipwhite(const char* q)
+{
+    const char* p = q;
+    while (isspace(*p)) ++p;
+    return p;
+}
+
+extern "C"
+{
+    double strtod(const char* str, char** end)
+    {
+        double d = 0.0;
+        int sign;
+        int n = 0;
+        const char *p, *a;
+
+        a = p = str;
+        p = skipwhite(p);
+
+        /* decimal part */
+        sign = 1;
+        if (*p == '-')
+        {
+            sign = -1;
+            ++p;
+        }
+        else if (*p == '+')
+            ++p;
+        if (isdigit(*p))
+        {
+            d = (double)(*p++ - '0');
+            while (*p && isdigit(*p))
+            {
+                d = d * 10.0 + (double)(*p - '0');
+                ++p;
+                ++n;
+            }
+            a = p;
+        }
+        else if (*p != '.')
+            goto done;
+        d *= sign;
+
+        /* fraction part */
+        if (*p == '.')
+        {
+            double f = 0.0;
+            double base = 0.1;
+            ++p;
+
+            if (isdigit(*p))
+            {
+                while (*p && isdigit(*p))
+                {
+                    f += base * (*p - '0');
+                    base /= 10.0;
+                    ++p;
+                    ++n;
+                }
+            }
+            d += f * sign;
+            a = p;
+        }
+
+        /* exponential part */
+        if ((*p == 'E') || (*p == 'e'))
+        {
+            int e = 0;
+            ++p;
+
+            sign = 1;
+            if (*p == '-')
+            {
+                sign = -1;
+                ++p;
+            }
+            else if (*p == '+')
+                ++p;
+
+            if (isdigit(*p))
+            {
+                while (*p == '0') ++p;
+                if (*p == '\0') --p;
+                e = (int)(*p++ - '0');
+                while (*p && isdigit(*p))
+                {
+                    e = e * 10 + (int)(*p - '0');
+                    ++p;
+                }
+                e *= sign;
+            }
+            else if (!isdigit(*(a - 1)))
+            {
+                a = str;
+                goto done;
+            }
+            else if (*p == 0)
+                goto done;
+
+            if (d == 2.2250738585072011 && e == -308)
+            {
+                d = 0.0;
+                a = p;
+                errno = ERANGE;
+                goto done;
+            }
+            if (d == 2.2250738585072012 && e <= -308)
+            {
+                d *= 1.0e-308;
+                a = p;
+                goto done;
+            }
+            d *= __builtin_powi(10.0, e);
+            a = p;
+        }
+        else if (p > str && !isdigit(*(p - 1)))
+        {
+            a = str;
+            goto done;
+        }
+
+    done:
+        if (end) *end = const_cast<char*>(a);
+        return d;
+    }
+}