initial commit

1 files changed, 52 insertions, 0 deletions

diff --git a/comp1521/smips/input.c b/comp1521/smips/input.c
new file mode 100644
index 0000000..0932978
--- /dev/null
+++ b/comp1521/smips/input.c
@@ -0,0 +1,52 @@
+#include "input.h"
+
+// Converts decimal values of a uint32_t argument to hex.
+uint32_t hex_to_decimal(const uint32_t decimal) {
+    uint32_t ret = 0;
+    for (size_t i = 0; i < sizeof(uint32_t); ++i) { // Iterate through 4 bytes.
+        uint32_t tmp = (decimal & (0xFFu << 8 * i)) >> 8 * i;
+        if (isalpha(tmp)) {
+            tmp -= 'a';
+            tmp += 10;
+        } else if (isdigit(tmp)) {
+            tmp -= '0';
+        }
+        // There should be no other cases if the input is hex.
+        ret |= (tmp << 4 * i);
+    }
+    return ret;
+}
+
+// Returns the next instruction in hex. Returns 0 if EOF reached.
+uint32_t get_next_instruction(FILE *const iptr) {
+    uint32_t ret = 0;
+    int i = 0;
+    for (int c = fgetc(iptr); c != '\n'; c = fgetc(iptr), ++i) {
+        if (c == EOF) {
+            return 0u;
+        }
+        uint32_t tmp = hex_to_decimal((uint32_t)c);
+        ret |= (tmp << (28 - i * 4));
+    }
+    // We have to take into account the potential for the hex value to not be
+    // "full", ie we may read abc instead of 00000abc.
+    ret >>= (32 - i * 4);
+    return ret;
+}
+
+// Sets the iptr to the previous instruction, which sits on the newline so that
+// later calls to get_next_instruction work as expected.
+// Also, if unable to find a previous instruction, sets the iptr to EOF.
+void goto_previous_instruction(FILE *const iptr) {
+    int c = 0;
+    fseek(iptr, -2L, SEEK_CUR);
+    while (ftell(iptr)) {
+        c = fgetc(iptr);
+        if (c == '\n') {
+            return;
+        }
+        fseek(iptr, -2L, SEEK_CUR);
+    }
+    // Start of file reached, out of bounds, so set EOF.
+    fseek(iptr, 0L, SEEK_END);
+}