add str_parse_dbl

2 files changed, 36 insertions, 0 deletions

diff --git a/stage3/string.c b/stage3/string.c
index ce776ad..c97330a 100644
--- a/stage3/string.c
+++ b/stage3/string.c
@@ -1,6 +1,7 @@
 #include "string.h"
 #include "memory.h"
 #include "heap.h"
+#include "math.h"
 
 isize str_cmp(str s1, str s2)
 {
@@ -54,6 +55,37 @@ usize str_parse_num(str s, u8 base, u64 *x)
     return s.len;
 }
 
+usize str_parse_dbl(str s, double *x)
+{
+	*x = 0.0;
+	str iter = s;
+
+	bool neg = false;
+	if (iter.len >= 1 && iter.data[0] == '-') {
+		neg = true;
+		iter = str_advance(iter, 1);
+	}
+
+	u64 tmp;
+	usize adv = str_parse_num(iter, 10, &tmp);
+	if (!adv)
+		return 0;
+
+	iter = str_advance(iter, adv);
+	*x = tmp;
+
+	if (iter.len >= 1 && iter.data[0] == '.'
+			&& (adv = str_parse_num(str_advance(iter, 1), 10, &tmp))) {
+		*x += (double) tmp / (double) ipow(10, adv);
+		iter = str_advance(iter, 1+adv);
+	}
+
+	if (neg)
+		*x = -*x;
+
+	return s.len - iter.len;
+}
+
 str str_walk(str *s, str sep)
 {
 	if (s->len == 0)
diff --git a/stage3/string.h b/stage3/string.h
index 1a28494..c5ceabe 100644
--- a/stage3/string.h
+++ b/stage3/string.h
@@ -17,6 +17,10 @@ usize str_find(str s, str tokens);
 // resulting number is stored in *x
 usize str_parse_num(str s, u8 base, u64 *x);
 
+// parses a double and returns number of chars processed
+// resulting number is stored in *x
+usize str_parse_dbl(str s, double *x);
+
 // this is a splitting function
 // returns the next non-empty substring of *s that is delimited by the tokens in sep
 // the returned string does not contain any of the separators