Use a normal quad-case for valueless /is4

When we don't have an immediate for the i-field in /is4, then use a
normal quad-bytecode encoding for it to save some small amount of
space and re-use existing machinery.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 6 insertions, 5 deletions

diff --git a/assemble.c b/assemble.c
index 17def3a..fd78b21 100644
--- a/assemble.c
+++ b/assemble.c
@@ -70,7 +70,7 @@
  *                 the 4-bit immediate from operand b in bits 3..0.
  * \173\xab      - the register number from operand a in bits 7..4, with
  *                 the value b in bits 3..0.
- * \174\a        - the register number from operand a in bits 7..4, and
+ * \174..\177    - the register number from operand 0..3 in bits 7..4, and
  *                 an arbitrary value in bits 3..0 (assembled as zero.)
  * \2ab          - a ModRM, calculated on EA in operand a, with the spare
  *                 field equal to digit b.
@@ -903,11 +903,14 @@ static int64_t calcsize(int32_t segment, int64_t offset, int bits,
 
         case 0172:
         case 0173:
-        case 0174:
             codes++;
             length++;
             break;
 
+        case4(0174):
+            length++;
+            break;
+
         case4(0250):
             length += is_sbyte32(opx) ? 1 : 4;
             break;
@@ -1495,9 +1498,7 @@ static void gencode(int32_t segment, int64_t offset, int bits,
             offset++;
             break;
 
-        case 0174:
-            c = *codes++;
-            opx = &ins->oprs[c];
+        case4(0174):
             bytes[0] = nasm_regvals[opx->basereg] << 4;
             out(offset, segment, bytes, OUT_RAWDATA, 1, NO_SEG, NO_SEG);
             offset++;