Refactor ARM halfword transfer

Author: hhhh1300

src/arm.c

@@ -265,32 +265,36 @@ int __zero(int rd)
     return __mov_i(__AL, rd, 0);
 }
 
+/* ARM halfword transfer (immediate offset) using special encoding
+ * For halfword: bits[11:8] = imm4H, bits[7:4] = encoding, bits[3:0] = imm4L
+ * imm4H: upper 4 bits of offset
+ * imm4L: lower 4 bits of offset
+ * encoding: 0b1011 for unsigned halfword, 0b1111 for signed halfword
+ */
 int arm_halfword_transfer(arm_cond_t cond,
                           int l,
                           arm_reg rn,
                           arm_reg rd,
-                          int ofs)
+                          int ofs,
+                          int signed_op)
 {
-    /* ARM halfword transfer using special encoding
-     * For halfword: bits[11:8] = imm4H, bits[3:0] = imm4L, bits[7,6,5,4] = 1SH1
-     */
     int opcode = 16 + 8 + 4 + l;
 
     if (ofs < 0) {
         opcode -= 8;
         ofs = -ofs;
     }
 
-    /* Halfword encoding: split offset into 4-bit high and low parts */
     if (ofs > 255) {
         error("Halfword offset too large");
     }
 
-    int imm4H = (ofs >> 4) & 0xF;
+    /* Halfword encoding: split offset into 4-bit high and low parts */
+    int imm4H = ((ofs >> 4) & 0xF) << 8;
     int imm4L = ofs & 0xF;
 
-    /* Encode with S=0, H=1 bits in lower 8 bits: 1011xxxx */
-    int encoded_ofs = (imm4H << 8) | 0xB0 | imm4L;
+    /* Encode lower 8 bits: 1011xxxx for unsigned, 1111xxxx for signed */
+    int encoded_ofs = imm4H | 0xB0 | imm4L | (signed_op << 6);
 
     return arm_encode(cond, opcode, rn, rd, encoded_ofs);
 }
@@ -332,34 +336,16 @@ int __sb(arm_cond_t cond, arm_reg rd, arm_reg rn, int ofs)
     return arm_transfer(cond, 0, 1, rn, rd, ofs);
 }
 
-int __luh(arm_cond_t cond, arm_reg rd, arm_reg rn, int ofs)
-{
-    return arm_halfword_transfer(cond, 1, rn, rd, ofs);
-}
-
+/* ARM signed halfword load (LDRSH) */
 int __lh(arm_cond_t cond, arm_reg rd, arm_reg rn, int ofs)
 {
-    /* ARM signed halfword load (LDRSH) */
-    int opcode = 16 + 8 + 4 + 1;
-    if (ofs < 0) {
-        opcode -= 8;
-        ofs = -ofs;
-    }
-
-    /* Halfword encoding: split offset into 4-bit high and low parts */
-    if (ofs > 255) {
-        fatal("Halfword offset too large");
-    }
-    int imm4H = (ofs >> 4) & 0xF;
-    int imm4L = ofs & 0xF;
-
-    int encoded_ofs = (imm4H << 8) | 0xF0 | imm4L;
-    return arm_encode(cond, opcode, rn, rd, encoded_ofs);
+    return arm_halfword_transfer(cond, 1, rn, rd, ofs, 1);
 }
 
+/* ARM halfword store (STRH) */
 int __sh(arm_cond_t cond, arm_reg rd, arm_reg rn, int ofs)
 {
-    return arm_halfword_transfer(cond, 0, rn, rd, ofs);
+    return arm_halfword_transfer(cond, 0, rn, rd, ofs, 0);
 }
 
 int __stmdb(arm_cond_t cond, int w, arm_reg rn, int reg_list)