fixed broken get_tarval_sub_bits() implementation: now correctly clip number of bits

[r15417]

ir/tv/strcalc.c

@@ -1268,13 +1268,17 @@ unsigned char sc_sub_bits(const void *value, int len, unsigned byte_ofs) {
 	unsigned char res;
 
 	/* the current scheme uses one byte to store a nibble */
-	if (nibble_ofs >= len)
+	if (4 * nibble_ofs >= len)
 		return 0;
 
 	res = _val(val[nibble_ofs]);
-	if (len > nibble_ofs + 1)
+	if (len > 4 * (nibble_ofs + 1))
 		res |= _val(val[nibble_ofs + 1]) << 4;
 
+	/* kick bits outsize */
+	if (len < 8*byte_ofs) {
+		res &= 0xFF >> (8*byte_ofs - len);
+	}
 	return res;
 }
 

ir/tv/strcalc.h

@@ -189,6 +189,14 @@ int sc_get_lowest_set_bit(const void *value);
 int sc_is_zero(const void *value);
 int sc_is_negative(const void *value);
 int sc_had_carry(void);
+
+/**
+ * Return the bits of a tarval at a given byte-offset.
+ *
+ * @param value     the value
+ * @param len       number of valid bits in the value
+ * @param byte_ofs  the byte offset
+ */
 unsigned char sc_sub_bits(const void *value, int len, unsigned byte_ofs);
 
 /**

ir/tv/tv.c

@@ -1479,7 +1479,7 @@ char *get_tarval_bitpattern(tarval *tv) {
 unsigned char get_tarval_sub_bits(tarval *tv, unsigned byte_ofs) {
 	switch (get_mode_arithmetic(tv->mode)) {
 	case irma_twos_complement:
-		return sc_sub_bits(tv->value, tv->length, byte_ofs);
+		return sc_sub_bits(tv->value, get_mode_size_bits(tv->mode), byte_ofs);
 	case irma_ieee754:
 		return fc_sub_bits(tv->value, get_mode_size_bits(tv->mode), byte_ofs);
 	default: