20060303a

1 files changed, 68 insertions, 0 deletions

diff --git a/libkern/charstod.c b/libkern/charstod.c
new file mode 100644
index 00000000..203e5379
--- /dev/null
+++ b/libkern/charstod.c
@@ -0,0 +1,68 @@
+#include <lib9.h>
+
+/*
+ * Reads a floating-point number by interpreting successive characters
+ * returned by (*f)(vp).  The last call it makes to f terminates the
+ * scan, so is not a character in the number.  It may therefore be
+ * necessary to back up the input stream up one byte after calling charstod.
+ */
+
+double
+charstod(int(*f)(void*), void *vp)
+{
+	double num, dem;
+	int neg, eneg, dig, exp, c;
+
+	num = 0;
+	neg = 0;
+	dig = 0;
+	exp = 0;
+	eneg = 0;
+
+	c = (*f)(vp);
+	while(c == ' ' || c == '\t')
+		c = (*f)(vp);
+	if(c == '-' || c == '+'){
+		if(c == '-')
+			neg = 1;
+		c = (*f)(vp);
+	}
+	while(c >= '0' && c <= '9'){
+		num = num*10 + c-'0';
+		c = (*f)(vp);
+	}
+	if(c == '.')
+		c = (*f)(vp);
+	while(c >= '0' && c <= '9'){
+		num = num*10 + c-'0';
+		dig++;
+		c = (*f)(vp);
+	}
+	if(c == 'e' || c == 'E'){
+		c = (*f)(vp);
+		if(c == '-' || c == '+'){
+			if(c == '-'){
+				dig = -dig;
+				eneg = 1;
+			}
+			c = (*f)(vp);
+		}
+		while(c >= '0' && c <= '9'){
+			exp = exp*10 + c-'0';
+			c = (*f)(vp);
+		}
+	}
+	exp -= dig;
+	if(exp < 0){
+		exp = -exp;
+		eneg = !eneg;
+	}
+	dem = pow10(exp);
+	if(eneg)
+		num /= dem;
+	else
+		num *= dem;
+	if(neg)
+		return -num;
+	return num;
+}