1 files changed, 141 insertions, 0 deletions
diff --git a/playground_05-25-2011.c b/playground_05-25-2011.c
new file mode 100644
index 0000000..20249a7
--- /dev/null
+++ b/playground_05-25-2011.c
@@ -0,0 +1,141 @@
+/*
+ * playground_05-25-2011.c
+ *
+ *
+ * Playing around with unions and macros, and how both
+ * of these things look in the memory
+ *
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+
+#define EXP(base, exp, ret) do {     \
+        int i;                       \
+        int acc = 1;                 \
+        for (i = 0; i < exp; i++)    \
+            acc *= base;             \
+        ret = acc;                   \
+    } while(0)                       \
+
+#define MUL(base, mult, ret) do {    \
+        int i;                       \
+        int acc = 0;                 \
+        for (i = 0; i < mult; i++)   \
+            acc += base;             \
+        ret = acc;                   \
+    } while(0)                       \
+
+/* trace a variable, requires ANSI compliant compiler */
+#define TRACE(var, fmt) \
+    printf("TRACE: " #var " = " #fmt ", %s:%d\n", var, __FILE__, __LINE__)
+
+#pragma pack(1)
+struct UART_tag
+{
+    union
+    {
+        struct
+        {
+            uint32_t baud_rate; /* bits [0:31] */
+
+            uint8_t tx_en : 1;
+            uint8_t rx_en : 1;
+            uint8_t parity : 1; /* bit [34], 35th */
+
+            uint32_t : 29;
+
+        } B;
+
+        uint64_t R;
+    } SET;
+
+};
+typedef struct UART_tag UART_t;
+
+void UART_info(UART_t *dev)
+{
+    printf("baud rate: %u\n"
+           "tx enabled: %s\n"
+           "rx enabled: %s\n"
+           "parity enabled: %s\n", dev->SET.B.baud_rate,
+                               dev->SET.B.tx_en ? "yes" : "no",
+                               dev->SET.B.rx_en ? "yes" : "no",
+                               dev->SET.B.parity ? "yes" : "no");
+}
+
+void dumpHex(UART_t *p, unsigned int sz)
+{
+    int i;
+    for (i = 0; i < sz; i++)
+    {
+        if (i % 4 == 0)
+            printf("%s0x%08x: ", i == 0 ? "" : "\n", i);
+
+        printf(" 0x%02x", ((unsigned char *) p)[i] );
+    }
+    printf("\n\n");
+}
+
+int main(int argc, char **argv)
+{
+    /* assigning a struct within the union */
+    puts("\t assigning a struct within the union");
+    UART_t myUart;
+	myUart.SET.R = 0;
+    myUart.SET.B.baud_rate = 19200;
+    myUart.SET.B.tx_en = 1;
+    myUart.SET.B.rx_en = 1;
+    myUart.SET.B.parity = 0;
+
+    UART_info(&myUart);
+    puts("");
+
+    puts("\t this is how UART_t looks in the memory");
+    dumpHex(&myUart, sizeof(UART_t));
+
+    /* disable a flag within the struct */
+    puts("\t disable a flag within the struct");
+    myUart.SET.B.tx_en = 0;
+    UART_info(&myUart);
+    puts("");
+
+    /* modifying the whole structure at once */
+    puts("\t modifying the whole structure at once");
+    myUart.SET.R = 0;
+    UART_info(&myUart);
+    puts("");
+
+    /* enable the parity bit */
+    myUart.SET.R |= (uint64_t) \
+                    ((uint64_t) 1 << (64 - 30)); /* this is inverted compared
+                                                  * to how it would be done on
+                                                  * a register */
+
+    puts("\t setting the parity bit to ON using logical OR operator");
+    UART_info(&myUart);
+    puts("");
+
+    printf("size of UART_t is: %lu bytes\n", sizeof(UART_t));
+    printf("size of UART_tag is: %lu bytes\n", sizeof(myUart.SET.B));
+
+    int x;
+    EXP(2, 20, x);
+    printf("a megabyte is %d bytes\n", x);
+
+    int y;
+    MUL(x, 4, y);
+    printf("4 megabytes is %d bytes\n", y);
+
+    /* endianess */
+    int z = 1;
+    if (*((unsigned char *) &z) == 1)
+        puts("machine has a little-endian byte ordering");
+    else
+        puts("machine has a big-endian byte ordering");
+
+    TRACE(y, %d);
+
+    return 0;
+}
+