From 5a72e2df2d68116241cf053b78a0f78135b02e7b Mon Sep 17 00:00:00 2001
From: Martin Ashby <martin@ashbysoft.com>
Date: Mon, 21 Nov 2022 20:25:15 +0000
Subject: Added ex4-2 and ex4-3

---
 ex4-2.c | 130 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 130 insertions(+)
 create mode 100644 ex4-2.c

(limited to 'ex4-2.c')

diff --git a/ex4-2.c b/ex4-2.c
new file mode 100644
index 0000000..8a57575
--- /dev/null
+++ b/ex4-2.c
@@ -0,0 +1,130 @@
+#include <stdio.h>
+
+/*static int _strlen(char s[]) {
+    int i;
+    for (i=0; s[i] != '\0'; i++) {}
+    return i;
+}*/
+
+/*static int _isspace(char s) {
+    return s == ' ' || s == '\t';
+}*/
+
+static int _isdigit(char s) {
+    return '0' <= s && s <= '9';
+}
+
+static int _abs(int a) {
+    if (a >=0) {
+        return a;
+    } else {
+        return -1 * a;
+    }
+}
+
+static int _intval(char s) {
+    return s - '0';
+}
+
+static int _isupper(char s) {
+    return 'A' <= s && s <= 'Z';
+}
+
+static char _tolower(char s) {
+    static int diff = 'A' - 'a';
+    if (_isupper(s)) {
+        return s - diff;
+    } else {
+        return s;
+    }
+}
+
+
+static int _atoi_internal(char s[], int n) {
+    if (s == NULL || *s == '\0' || !_isdigit(*s)) {
+        return n;
+    }
+    __attribute__((musttail)) // Functional programinng enabler :) 
+    return _atoi_internal(s + 1, (10 * n) + _intval(*s));
+}
+/**
+ * Converts a string to an integer
+ * string must be null terminated
+ * overflow isn't detected, int is the limit
+ */ 
+int _atoi(char s[]) {
+    int i = 0;
+    int sign = (s[i] == '-') ? -1 : 1;
+    if (s[i] == '+' || s[i] == '-')
+        i++;
+    return _atoi_internal(s + i, 0) * sign;
+}
+
+/**
+ * Converts a string to a double
+ * 
+ * string must be null terminated.
+ * overflow isn't detected, and double precision is the limit.
+ */
+double _atof(char s[]) {
+    double val, power, ee;
+    int i = 0;
+    int sign = (s[i] == '-') ? -1 : 1;
+    if (s[i] == '+' || s[i] == '-')
+        i++;
+    for (val = 0.0; _isdigit(s[i]); i++)
+        val = 10.0 * val + _intval(s[i]);
+    if (s[i] == '.')
+        i++;
+    for (power = 1.0; _isdigit(s[i]); i++) {
+        val = 10.0 * val + _intval(s[i]);
+        power *= 10.0;
+    }
+    ee = 1.0;
+    if (_tolower(s[i]) == 'e') {
+        i++;
+        int exponent = _atoi(s + i);
+        if (exponent >= 0) {
+            for (int j=0;j<_abs(exponent);j++) ee *= 10.0;
+        } else {
+            for (int j=0;j<_abs(exponent);j++) ee /= 10.0;
+        }
+    }
+    return (sign * val / power) * ee;
+
+}
+
+void testb(char s[]) {
+    printf("atoi s = [%s] result = [%d]\n", s, _atoi(s));
+}
+
+void test(char s[]) {
+    printf("atof s = [%s] result = [%lf]\n", s, _atof(s));
+}
+
+int main(void) {
+    test("");
+    test("gibber");
+    test("\0");
+    test("1");
+    test("1.0");
+    test("99.0");
+    test("-10.0");
+    test("+11.0");
+    test("++11.0");
+    test("-11111111111111111111111111111111111111111111111111111111111111111111111111111111111.1");
+
+    testb("gibber");
+    testb("");
+    testb("\0");
+    testb("1");
+    testb("1.5");
+    testb("+2.6");
+    testb("-7.8");
+    testb("--7.8");
+    
+    test("+11.0e5");
+    test("2.75345e3");
+    test("2.75345e-3");
+    test("2.75345E-3");
+}
\ No newline at end of file
-- 
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