From 77bdaaf8533959dd03f8a85882f7150b9f874f5f Mon Sep 17 00:00:00 2001
From: Steve Karg <skarg@users.sourceforge.net>
Date: Tue, 4 Feb 2025 13:56:53 -0600
Subject: [PATCH] Fixed usage of 8-bit modulo operator off-by-one maximum.
 (#901)

---
 ports/stm32f4xx/device.c                 | 2 +-
 src/bacnet/datalink/bsc/bsc-util.c       | 4 ++--
 src/bacnet/datalink/mstp.c               | 2 +-
 test/bacnet/basic/sys/ringbuf/src/main.c | 4 ++--
 test/bacnet/datalink/cobs/src/main.c     | 2 +-
 5 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/ports/stm32f4xx/device.c b/ports/stm32f4xx/device.c
index 0ccfff10..c5d0c901 100644
--- a/ports/stm32f4xx/device.c
+++ b/ports/stm32f4xx/device.c
@@ -474,7 +474,7 @@ void Device_UUID_Init(void)
 
     /* 1. Generate 16 random bytes = 128 bits */
     for (i = 0; i < sizeof(Device_UUID); i++) {
-        Device_UUID[i] = rand() % 255;
+        Device_UUID[i] = rand() % 256;
     }
     /* 2. Adjust certain bits according to RFC 4122 section 4.4.
        This just means do the following
diff --git a/src/bacnet/datalink/bsc/bsc-util.c b/src/bacnet/datalink/bsc/bsc-util.c
index a13e3ff7..4c217de8 100644
--- a/src/bacnet/datalink/bsc/bsc-util.c
+++ b/src/bacnet/datalink/bsc/bsc-util.c
@@ -97,7 +97,7 @@ void bsc_generate_random_vmac(BACNET_SC_VMAC_ADDRESS *p)
     int i;
 
     for (i = 0; i < BVLC_SC_VMAC_SIZE; i++) {
-        p->address[i] = rand() % 255;
+        p->address[i] = rand() % 256;
         if (i == 0) {
             /* According H.7.3 EUI-48 and Random-48 VMAC Address:
                The Random-48 VMAC is a 6-octet VMAC address in which the least
@@ -120,7 +120,7 @@ void bsc_generate_random_uuid(BACNET_SC_UUID *p)
     int i;
 
     for (i = 0; i < BVLC_SC_UUID_SIZE; i++) {
-        p->uuid[i] = rand() % 255;
+        p->uuid[i] = rand() % 256;
     }
     debug_printf_hex(0, p->uuid, BVLC_SC_UUID_SIZE, "bsc_generate_random_uuid");
 }
diff --git a/src/bacnet/datalink/mstp.c b/src/bacnet/datalink/mstp.c
index c9dbdc5d..9e3ef0d2 100644
--- a/src/bacnet/datalink/mstp.c
+++ b/src/bacnet/datalink/mstp.c
@@ -1352,7 +1352,7 @@ void MSTP_Zero_Config_UUID_Init(struct mstp_port_struct_t *mstp_port)
     }
     /* 1. Generate 16 random bytes = 128 bits */
     for (i = 0; i < MSTP_UUID_SIZE; i++) {
-        mstp_port->UUID[i] = rand() % 255;
+        mstp_port->UUID[i] = rand() % 256;
     }
     /* 2. Adjust certain bits according to RFC 4122 section 4.4.
        This just means do the following
diff --git a/test/bacnet/basic/sys/ringbuf/src/main.c b/test/bacnet/basic/sys/ringbuf/src/main.c
index c0cd2925..cce9f05c 100644
--- a/test/bacnet/basic/sys/ringbuf/src/main.c
+++ b/test/bacnet/basic/sys/ringbuf/src/main.c
@@ -45,7 +45,7 @@ static void testRingAroundBuffer(
     /* test the ring around the buffer */
     for (index = 0; index < element_count; index++) {
         for (count = 1; count < 4; count++) {
-            value = (index * count) % 255;
+            value = (index * count) % 256;
             for (data_index = 0; data_index < element_size; data_index++) {
                 data_element[data_index] = value;
             }
@@ -54,7 +54,7 @@ static void testRingAroundBuffer(
             zassert_equal(Ringbuf_Count(test_buffer), count, NULL);
         }
         for (count = 1; count < 4; count++) {
-            value = (index * count) % 255;
+            value = (index * count) % 256;
             test_data = Ringbuf_Peek(test_buffer);
             zassert_not_null(test_data, NULL);
             if (test_data) {
diff --git a/test/bacnet/datalink/cobs/src/main.c b/test/bacnet/datalink/cobs/src/main.c
index 2750d55e..dfad9496 100644
--- a/test/bacnet/datalink/cobs/src/main.c
+++ b/test/bacnet/datalink/cobs/src/main.c
@@ -38,7 +38,7 @@ static void test_COBS_Encode_Decode(void)
     size_t encoded_buffer_length, test_buffer_length;
 
     for (i = 2; i < sizeof(buffer); i++) {
-        buffer[i] = i % 0xff;
+        buffer[i] = i % 256;
     }
     encoded_buffer_length = cobs_frame_encode(
         encoded_buffer, sizeof(encoded_buffer), buffer, sizeof(buffer));