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firmware: sniffer: fix ~INS procedure byte comparison

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(~g_tpdu.packet[1]) == byte can never be true.
Unary ~ applies the integer promotions first,
so for tpdu INS = 0xA4 lhs should be 0x5B but as int
it gets zero extended to at least 16 bits and then flipped,
so it is 0xFFFFFF5B = -165, byte promotes to 0..255.

The ack was therefore dead code -> fallthrough to SW1
branch, fails 0x6x/0x9x test, TPDU gets flagged
SNIFF_DATA_FLAG_ERROR_MALFORMED from what I can tell.
But I am losing track of all these arcane issues to be honest.

Narrow the complement back to 8 bits.
Fyi this is unrelated to signedness and not specific to ARM.

Change-Id: I800f50ef35356429d07aa685ea919e70ec34946e
This commit is contained in:
Eric Wild
2026-07-28 17:42:32 +02:00
committed by lynxis lazus
parent 58438bfdbc
commit 2ade068fb6
1 changed files with 1 additions and 1 deletions
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firmware/libcommon/source/sniffer.c
+1 -1
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@@ -775,7 +775,7 @@ static void process_byte_tpdu(uint8_t byte)
} else if (g_tpdu.packet[1] == byte) { /* get all remaining data bytes */
change_tpdu_state(TPDU_S_DATA_REMAINING);
break;
} else if ((~g_tpdu.packet[1]) == byte) { /* get single data byte */
} else if ((uint8_t)(~g_tpdu.packet[1]) == byte) { /* get single data byte */
change_tpdu_state(TPDU_S_DATA_SINGLE);
break;
}