Fix float endianness issue on big endian architecture.

It converts float values depending on what order they come in.

This patch was modified from rm5248 [1]

[1] https://github.com/synexxus/libmodbus/commit/a511768e7fe7ec52d7bae1d9ae04e33f87a59627

src/modbus-data.c

@@ -123,9 +123,18 @@ float modbus_get_float_abcd(const uint16_t *src)
 {
     float f;
     uint32_t i;
+    uint8_t a, b, c, d;
 
-    i = ntohl(((uint32_t)src[0] << 16) + src[1]);
-    memcpy(&f, &i, sizeof(float));
+    a = (src[0] >> 8) & 0xFF;
+    b = (src[0] >> 0) & 0xFF;
+    c = (src[1] >> 8) & 0xFF;
+    d = (src[1] >> 0) & 0xFF;
+
+    i = (a << 24) |
+        (b << 16) |
+        (c << 8) |
+        (d << 0);
+    memcpy(&f, &i, 4);
 
     return f;
 }
@@ -135,9 +144,18 @@ float modbus_get_float_dcba(const uint16_t *src)
 {
     float f;
     uint32_t i;
+    uint8_t a, b, c, d;
 
-    i = ntohl(bswap_32((((uint32_t)src[0]) << 16) + src[1]));
-    memcpy(&f, &i, sizeof(float));
+    a = (src[0] >> 8) & 0xFF;
+    b = (src[0] >> 0) & 0xFF;
+    c = (src[1] >> 8) & 0xFF;
+    d = (src[1] >> 0) & 0xFF;
+
+    i = (d << 24) |
+        (c << 16) |
+        (b << 8) |
+        (a << 0);
+    memcpy(&f, &i, 4);
 
     return f;
 }
@@ -147,9 +165,18 @@ float modbus_get_float_badc(const uint16_t *src)
 {
     float f;
     uint32_t i;
+    uint8_t a, b, c, d;
 
-    i = ntohl((uint32_t)(bswap_16(src[0]) << 16) + bswap_16(src[1]));
-    memcpy(&f, &i, sizeof(float));
+    a = (src[0] >> 8) & 0xFF;
+    b = (src[0] >> 0) & 0xFF;
+    c = (src[1] >> 8) & 0xFF;
+    d = (src[1] >> 0) & 0xFF;
+
+    i = (b << 24) |
+        (a << 16) |
+        (d << 8) |
+        (c << 0);
+    memcpy(&f, &i, 4);
 
     return f;
 }
@@ -159,9 +186,18 @@ float modbus_get_float_cdab(const uint16_t *src)
 {
     float f;
     uint32_t i;
+    uint8_t a, b, c, d;
 
-    i = ntohl((((uint32_t)src[1]) << 16) + src[0]);
-    memcpy(&f, &i, sizeof(float));
+    a = (src[0] >> 8) & 0xFF;
+    b = (src[0] >> 0) & 0xFF;
+    c = (src[1] >> 8) & 0xFF;
+    d = (src[1] >> 0) & 0xFF;
+
+    i = (c << 24) |
+        (d << 16) |
+        (a << 8) |
+        (b << 0);
+    memcpy(&f, &i, 4);
 
     return f;
 }
@@ -176,50 +212,84 @@ float modbus_get_float(const uint16_t *src)
     memcpy(&f, &i, sizeof(float));
 
     return f;
+
 }
 
 /* Set a float to 4 bytes for Modbus w/o any conversion (ABCD) */
 void modbus_set_float_abcd(float f, uint16_t *dest)
 {
     uint32_t i;
+    uint8_t *out = (uint8_t*) dest;
+    uint8_t a, b, c, d;
 
     memcpy(&i, &f, sizeof(uint32_t));
-    i = htonl(i);
-    dest[0] = (uint16_t)(i >> 16);
-    dest[1] = (uint16_t)i;
+    a = (i >> 24) & 0xFF;
+    b = (i >> 16) & 0xFF;
+    c = (i >> 8) & 0xFF;
+    d = (i >> 0) & 0xFF;
+
+    out[0] = a;
+    out[1] = b;
+    out[2] = c;
+    out[3] = d;
 }
 
 /* Set a float to 4 bytes for Modbus with byte and word swap conversion (DCBA) */
 void modbus_set_float_dcba(float f, uint16_t *dest)
 {
     uint32_t i;
+    uint8_t *out = (uint8_t*) dest;
+    uint8_t a, b, c, d;
 
     memcpy(&i, &f, sizeof(uint32_t));
-    i = bswap_32(htonl(i));
-    dest[0] = (uint16_t)(i >> 16);
-    dest[1] = (uint16_t)i;
+    a = (i >> 24) & 0xFF;
+    b = (i >> 16) & 0xFF;
+    c = (i >> 8) & 0xFF;
+    d = (i >> 0) & 0xFF;
+
+    out[0] = d;
+    out[1] = c;
+    out[2] = b;
+    out[3] = a;
+
 }
 
 /* Set a float to 4 bytes for Modbus with byte swap conversion (BADC) */
 void modbus_set_float_badc(float f, uint16_t *dest)
 {
     uint32_t i;
+    uint8_t *out = (uint8_t*) dest;
+    uint8_t a, b, c, d;
 
     memcpy(&i, &f, sizeof(uint32_t));
-    i = htonl(i);
-    dest[0] = (uint16_t)bswap_16(i >> 16);
-    dest[1] = (uint16_t)bswap_16(i & 0xFFFF);
+    a = (i >> 24) & 0xFF;
+    b = (i >> 16) & 0xFF;
+    c = (i >> 8) & 0xFF;
+    d = (i >> 0) & 0xFF;
+
+    out[0] = b;
+    out[1] = a;
+    out[2] = d;
+    out[3] = c;
 }
 
 /* Set a float to 4 bytes for Modbus with word swap conversion (CDAB) */
 void modbus_set_float_cdab(float f, uint16_t *dest)
 {
     uint32_t i;
+    uint8_t *out = (uint8_t*) dest;
+    uint8_t a, b, c, d;
 
     memcpy(&i, &f, sizeof(uint32_t));
-    i = htonl(i);
-    dest[0] = (uint16_t)i;
-    dest[1] = (uint16_t)(i >> 16);
+    a = (i >> 24) & 0xFF;
+    b = (i >> 16) & 0xFF;
+    c = (i >> 8) & 0xFF;
+    d = (i >> 0) & 0xFF;
+
+    out[0] = c;
+    out[1] = d;
+    out[2] = a;
+    out[3] = b;
 }
 
 /* DEPRECATED - Set a float to 4 bytes in a sort of Modbus format! */

tests/unit-test-client.c

@@ -27,6 +27,7 @@ int send_crafted_request(modbus_t *ctx, int function,
                          uint16_t max_value, uint16_t bytes,
                          int backend_length, int backend_offset);
 int equal_dword(uint16_t *tab_reg, const uint32_t value);
+int is_memory_equal(const void *s1, const void *s2, size_t size);
 
 #define BUG_REPORT(_cond, _format, _args ...) \
     printf("\nLine %d: assertion error for '%s': " _format "\n", __LINE__, # _cond, ## _args)
@@ -40,6 +41,11 @@ int equal_dword(uint16_t *tab_reg, const uint32_t value);
     }                                             \
 };
 
+int is_memory_equal(const void *s1, const void *s2, size_t size)
+{
+    return (memcmp(s1, s2, size) == 0);
+}
+
 int equal_dword(uint16_t *tab_reg, const uint32_t value) {
     return ((tab_reg[0] == (value >> 16)) && (tab_reg[1] == (value & 0xFFFF)));
 }
@@ -287,26 +293,26 @@ int main(int argc, char *argv[])
     /** FLOAT **/
     printf("1/4 Set/get float ABCD: ");
     modbus_set_float_abcd(UT_REAL, tab_rp_registers);
-    ASSERT_TRUE(equal_dword(tab_rp_registers, UT_IREAL_ABCD), "FAILED Set float ABCD");
-    real = modbus_get_float_abcd(tab_rp_registers);
+    ASSERT_TRUE(is_memory_equal(tab_rp_registers, UT_IREAL_ABCD_SET, 4), "FAILED Set float ABCD");
+    real = modbus_get_float_abcd(UT_IREAL_ABCD_GET);
     ASSERT_TRUE(real == UT_REAL, "FAILED (%f != %f)\n", real, UT_REAL);
 
     printf("2/4 Set/get float DCBA: ");
     modbus_set_float_dcba(UT_REAL, tab_rp_registers);
-    ASSERT_TRUE(equal_dword(tab_rp_registers, UT_IREAL_DCBA), "FAILED Set float DCBA");
-    real = modbus_get_float_dcba(tab_rp_registers);
+    ASSERT_TRUE(is_memory_equal(tab_rp_registers, UT_IREAL_DCBA_SET, 4), "FAILED Set float DCBA");
+    real = modbus_get_float_dcba(UT_IREAL_DCBA_GET);
     ASSERT_TRUE(real == UT_REAL, "FAILED (%f != %f)\n", real, UT_REAL);
 
     printf("3/4 Set/get float BADC: ");
     modbus_set_float_badc(UT_REAL, tab_rp_registers);
-    ASSERT_TRUE(equal_dword(tab_rp_registers, UT_IREAL_BADC), "FAILED Set float BADC");
-    real = modbus_get_float_badc(tab_rp_registers);
+    ASSERT_TRUE(is_memory_equal(tab_rp_registers, UT_IREAL_BADC_SET, 4), "FAILED Set float BADC");
+    real = modbus_get_float_badc(UT_IREAL_BADC_GET);
     ASSERT_TRUE(real == UT_REAL, "FAILED (%f != %f)\n", real, UT_REAL);
 
     printf("4/4 Set/get float CDAB: ");
     modbus_set_float_cdab(UT_REAL, tab_rp_registers);
-    ASSERT_TRUE(equal_dword(tab_rp_registers, UT_IREAL_CDAB), "FAILED Set float CDAB");
-    real = modbus_get_float_cdab(tab_rp_registers);
+    ASSERT_TRUE(is_memory_equal(tab_rp_registers, UT_IREAL_CDAB_SET, 4), "FAILED Set float CDAB");
+    real = modbus_get_float_cdab(UT_IREAL_CDAB_GET);
     ASSERT_TRUE(real == UT_REAL, "FAILED (%f != %f)\n", real, UT_REAL);
 
     printf("\nAt this point, error messages doesn't mean the test has failed\n");

tests/unit-test.h.in

@@ -56,12 +56,45 @@ const uint16_t UT_INPUT_REGISTERS_ADDRESS = 0x108;
 const uint16_t UT_INPUT_REGISTERS_NB = 0x1;
 const uint16_t UT_INPUT_REGISTERS_TAB[] = { 0x000A };
 
+/*
+ * This float value is 0x47F12000 (in big-endian format).
+ * In Little-endian(intel) format, it will be stored in memory as follows:
+ * 0x00 0x20 0xF1 0x47
+ *
+ * You can check this with the following code:
+
+   float fl = UT_REAL;
+   uint8_t *inmem = (uint8_t*)&fl;
+   int x;
+   for(x = 0; x < 4; x++){
+       printf("0x%02X ", inmem[ x ]);
+   }
+   printf("\n");
+ */
 const float UT_REAL = 123456.00;
 
-const uint32_t UT_IREAL_ABCD = 0x0020F147;
-const uint32_t UT_IREAL_DCBA = 0x47F12000;
-const uint32_t UT_IREAL_BADC = 0x200047F1;
-const uint32_t UT_IREAL_CDAB = 0xF1470020;
+/*
+ * The following arrays assume that 'A' is the MSB,
+ * and 'D' is the LSB.
+ * Thus, the following is the case:
+ * A = 0x47
+ * B = 0xF1
+ * C = 0x20
+ * D = 0x00
+ *
+ * There are two sets of arrays: one to test that the setting is correct,
+ * the other to test that the getting is correct.
+ * Note that the 'get' values must be constants in processor-endianness,
+ * as libmodbus will convert all words to processor-endianness as they come in.
+ */
+const uint8_t UT_IREAL_ABCD_SET[] = {0x47, 0xF1, 0x20, 0x00};
+const uint16_t UT_IREAL_ABCD_GET[] = {0x47F1, 0x2000};
+const uint8_t UT_IREAL_DCBA_SET[] = {0x00, 0x20, 0xF1, 0x47};
+const uint16_t UT_IREAL_DCBA_GET[] = {0x0020, 0xF147};
+const uint8_t UT_IREAL_BADC_SET[] = {0xF1, 0x47, 0x00, 0x20};
+const uint16_t UT_IREAL_BADC_GET[] = {0xF147, 0x0020};
+const uint8_t UT_IREAL_CDAB_SET[] = {0x20, 0x00, 0x47, 0xF1};
+const uint16_t UT_IREAL_CDAB_GET[] = {0x2000, 0x47F1};
 
 /* const uint32_t UT_IREAL_ABCD = 0x47F12000);
 const uint32_t UT_IREAL_DCBA = 0x0020F147;