From b2ce577f4acf98a8efc474a8099de661af54fde7 Mon Sep 17 00:00:00 2001
From: Lev Walkin <vlm@lionet.info>
Date: Wed, 18 Aug 2004 08:23:43 +0000
Subject: [PATCH] proper computations
---
skeletons/ber_tlv_tag.c | 31 ++++++++++++++-----------------
1 file changed, 14 insertions(+), 17 deletions(-)
diff --git a/skeletons/ber_tlv_tag.c b/skeletons/ber_tlv_tag.c
index 2664b906..f7df191f 100644
--- a/skeletons/ber_tlv_tag.c
+++ b/skeletons/ber_tlv_tag.c
@@ -104,7 +104,7 @@ der_tlv_tag_serialize(ber_tlv_tag_t tag, void *bufp, size_t size) {
ber_tlv_tag_t tval = BER_TAG_VALUE(tag);
uint8_t *buf = (uint8_t *)bufp;
uint8_t *end;
- size_t computed_size;
+ size_t required_size;
int i;
if(tval <= 30) {
@@ -118,29 +118,26 @@ der_tlv_tag_serialize(ber_tlv_tag_t tag, void *bufp, size_t size) {
/*
* Compute the size of the subsequent bytes.
- * The routine is written so every floating-point
- * operation is done at compile time.
- * Note, there is a subtle problem lurking here,
- * could you guess where it is? :)
- * Hint: what happens when ((8*sizeof(tag))%7) == 0?
*/
- computed_size = 1 + 8 * sizeof(tag) / 7;
- for(i = (8*sizeof(tag)) - ((8*sizeof(tag))%7); i >= 7; i -= 7) {
- if((tval >> i) & 0x7F) break;
- computed_size--;
+ for(required_size = 1, i = 7; i < 8 * sizeof(tag); i += 7) {
+ if(tag >> i)
+ required_size++;
+ else
+ break;
}
+ if(size < required_size)
+ return required_size + 1;
+
/*
* Fill in the buffer, space permitting.
*/
- if(size > computed_size)
- end = buf + computed_size;
- else
- end = buf + size;
- for((void)i; buf < end; i -= 7, buf++) {
- *buf = 0x80 | ((tval>>i) & 0x7F);
+ end = buf + required_size - 1;
+ for(i -= 7; buf <= end; i -= 7, buf++) {
+ *buf = 0x80 | ((tval >> i) & 0x7F);
}
+ *end &= 0x7F; /* Clear the last high bit */
- return computed_size + 1;
+ return required_size + 1;
}
--
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