Implement real parsing and formatting

Makefile

@@ -4,6 +4,7 @@ NAME=abCalc
 all: $(NAME)
 
 abCalcExpr.o: abCalcExpr.h
+abCalcExprReal.o: abCalcExpr.h
 abCalcStack.o: abCalcExpr.h abCalcStack.h
 
 $(NAME): $(OBJS)

abCalcExprReal.c

@@ -0,0 +1,98 @@
+/* 
+    abCalcExprReal.c
+        By: Jeremy Rand
+ */
+
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include "abCalcExpr.h"
+
+
+static abCalcExpr *abCalcExprRealParse(abCalcExpr *expr, char *buffer);
+static char *abCalcExprRealFormat(abCalcExpr *expr, char *buffer);
+
+
+static abCalcExprCallbacks gCallbacks = {
+    abCalcExprRealParse,
+    abCalcExprRealFormat
+};
+
+
+abCalcExpr *abCalcExprRealParse(abCalcExpr *expr, char *buffer)
+{
+    int offset;
+    int expOffset = -1;
+    int periodOffset = -1;
+    int len;
+
+    /* First validate */
+    if (buffer == NULL)
+        return NULL;
+
+    len = strlen(buffer);
+
+    for (offset = 0; offset < len; offset++) {
+        switch (buffer[offset]) {
+            case '0':
+            case '1':
+            case '2':
+            case '3':
+            case '4':
+            case '5':
+            case '6':
+            case '7':
+            case '8':
+            case '9':
+                break;
+
+            case '.':
+                if (periodOffset != -1)
+                    return NULL;
+                periodOffset = offset;
+                break;
+
+            case '-':
+                if (offset == 0)
+                    break;
+                /* Fallthrough */
+            case '+':
+                if ((expOffset == -1) ||
+                    ((expOffset + 1) != offset))
+                    return NULL;
+                break;
+
+            case 'e':
+            case 'E':
+                if (expOffset != -1)
+                    return NULL;
+                expOffset = offset;
+                break;
+
+            default:
+                return NULL;
+        }
+    }
+    
+    expr->type = abCalcExprTypeReal;
+    expr->u.real = atof(buffer);
+    return expr;
+}
+
+
+char *abCalcExprRealFormat(abCalcExpr *expr, char *buffer)
+{
+    if (expr == NULL)
+        return NULL;
+
+    if (buffer == NULL)
+        return NULL;
+
+    if (expr->type != abCalcExprTypeReal)
+        return NULL;
+
+    sprintf(buffer, "%f", expr->u.real);
+    return buffer;
+}