diff --git a/code/duffle/gte.h b/code/duffle/gte.h
index 2e5ce78..502443d 100644
--- a/code/duffle/gte.h
+++ b/code/duffle/gte.h
@@ -177,18 +177,17 @@ enum {
  * Mirrors the OPCODE_SHIFT / RS_SHIFT convention used in mips.h.
  */
 
-	gte_shift_sf  = 19,  gte_width_sf  = 1,  gte_mask_sf  = 0x1,
-	gte_shift_mx  = 17,  gte_width_mx  = 2,  gte_mask_mx  = 0x3,
-	gte_shift_v   = 15,  gte_width_v   = 2,  gte_mask_v   = 0x3,
-	gte_shift_cv  = 13,  gte_width_cv  = 2,  gte_mask_cv = 0x3,
-	gte_shift_lm  = 10,  gte_width_lm  = 1,  gte_mask_lm  = 0x1,
-	gte_shift_cmd =  0,  gte_width_cmd = 6,  gte_mask_cmd = 0x3F,
+	gte_shift_sf  = 19,  gte_width_sf  = 1,
+	gte_shift_mx  = 17,  gte_width_mx  = 2,
+	gte_shift_v   = 15,  gte_width_v   = 2,
+	gte_shift_cv  = 13,  gte_width_cv  = 2,
+	gte_shift_lm  = 10,  gte_width_lm  = 1,
+	gte_shift_cmd =  0,  gte_width_cmd = 6,
 
 	/* Fake command number (bits 24-20) — IGNORED by the GTE hardware per PSX-SPX `geometrytransformationenginegte.md` line 48.
 	 * libgte's compiler emits non-zero values in this field as a disassembly signature. */
 	gte_shift_fake_cmd = 20,
 	gte_width_fake_cmd = 5,
-	gte_mask_fake_cmd  = 0x1F,
 };
 
 /* --- GTE Control Register Aliases (Pitfall 1) ---
@@ -351,13 +350,13 @@ enum { _C2_TX_SUBS_ = 0
 #define gte_cmd_base (enc_op(op_cop2) | (1 << 25))
 
 /* Per-field encoders. Each one does (value & mask) << shift on its own. */
-#define enc_gte_sf(sf)          (((sf)  & gte_mask_sf      ) << gte_shift_sf )
-#define enc_gte_mx(mx)          (((mx)  & gte_mask_mx      ) << gte_shift_mx )
-#define enc_gte_v(v)            (((v)   & gte_mask_v       ) << gte_shift_v  )
-#define enc_gte_cv(cv)          (((cv)  & gte_mask_cv      ) << gte_shift_cv )
-#define enc_gte_lm(lm)          (((lm)  & gte_mask_lm      ) << gte_shift_lm )
-#define enc_gte_cmd(cmd)        (((cmd) & gte_mask_cmd     ) << gte_shift_cmd )
-#define enc_gte_fake_cmd(x)     (((x)   & gte_mask_fake_cmd) << gte_shift_fake_cmd)
+#define enc_gte_sf(sf)          ((sf)  << gte_shift_sf )
+#define enc_gte_mx(mx)          ((mx)  << gte_shift_mx )
+#define enc_gte_v(v)            ((v)   << gte_shift_v  )
+#define enc_gte_cv(cv)          ((cv)  << gte_shift_cv )
+#define enc_gte_lm(lm)          ((lm)  << gte_shift_lm )
+#define enc_gte_cmd(cmd)        ((cmd) << gte_shift_cmd )
+#define enc_gte_fake_cmd(x)     ((x)   << gte_shift_fake_cmd)
 
 /* Composite: all six GTE fields + the COP2/CO base. */
 #define enc_gte_cmdw(sf, mx, v, cv, lm, cmd) ( \
diff --git a/code/duffle/math.h b/code/duffle/math.h
index 4eefeff..64a35bf 100644
--- a/code/duffle/math.h
+++ b/code/duffle/math.h
@@ -24,6 +24,7 @@ enum {
 };
 
 typedef Array_(U1, 2);
+typedef Array_(U2, 2);
 typedef Array_(U4, 2);
 typedef Array_(S2, 2);
 typedef Array_(S2, 3);
@@ -46,6 +47,9 @@ typedef Struct_(V4_S4)      { S4 x; S4 y; S4 z; S4 w; };
 // typedef Struct_(P3_S4)      { S4 x; S4 y; S4 z; S4 w1; }; // RGA(Lengyel): Affine point with implicit weight one. Storage alias of V3_S4. Use P3_S4 when the value is a point.
 typedef V3_S4 P3_S4;
 
+typedef Struct_(R1_U2) { U2 p0; U2 p1; };
+typedef Struct_(R1_S2) { S2 p0; S2 p1; };
+
 typedef Struct_(R2_S2)      { V2_S2 p0; V2_S2 p1; }; // Range-2 Signed 2-Byte (16-bit)
 typedef Struct_(R2_S4)      { V2_S4 p0; V2_S4 p1; }; // Range-2 Signed 4-Byte (32-bit)
 
@@ -64,6 +68,8 @@ typedef Array_(V2_S2, 2);
 typedef Array_(V2_S2, 3);
 typedef Array_(V2_S2, 4);
 
+#define r1u2(p0,p1) (R1_U2){p0,p1}
+
 enum {
 	fp_one = (1 << 12),
 };
diff --git a/code/duffle/mips.h b/code/duffle/mips.h
index e283b57..59f0d73 100644
--- a/code/duffle/mips.h
+++ b/code/duffle/mips.h
@@ -259,22 +259,22 @@ enum { _BitOffsets = 0
 	, SHAMT_SHIFT  = 6  /* Shift Amount */
 	, FC_SHIFT     = 0
 
-/* Bit Masks to prevent overflow into adjacent fields */
+/* IMM_MASK is the 16-bit two's-complement truncation for the immediate field.
+ * It is NOT a range guard — it is load-bearing for negative branch offsets
+ * (the metaprogram emits raw signed offsets; the mask truncates them to the
+ * 16-bit representation the hardware expects). The static analysis
+ * `immediate_field_width` check validates ranges at build time. */
 
-	, OPCODE_MASK  = 0x3F
-	, REG_MASK     = 0x1F
-	, SHAMT_MASK   = 0x1F /* Shift Amount */
-	, FC_MASK      = 0x3F
 	, IMM_MASK     = 0xFFFF
 };
 
-#define enc_op(op)       (((op)    & OPCODE_MASK) << OPCODE_SHIFT)
-#define enc_rs(rs)       (((rs)    & REG_MASK)    << RS_SHIFT)
-#define enc_rt(rt)       (((rt)    & REG_MASK)    << RT_SHIFT)
-#define enc_rd(rd)       (((rd)    & REG_MASK)    << RD_SHIFT)
-#define enc_shamt(shamt) (((shamt) & SHAMT_MASK)  << SHAMT_SHIFT)
-#define enc_fc(fc)       (((fc)    & FC_MASK)     << FC_SHIFT)
-#define enc_imm(imm)     (((imm)   & IMM_MASK))
+#define enc_op(op)       ((op)    << OPCODE_SHIFT)
+#define enc_rs(rs)       ((rs)    << RS_SHIFT)
+#define enc_rt(rt)       ((rt)    << RT_SHIFT)
+#define enc_rd(rd)       ((rd)    << RD_SHIFT)
+#define enc_shamt(shamt) ((shamt) << SHAMT_SHIFT)
+#define enc_fc(fc)       ((fc)    << FC_SHIFT)
+#define enc_imm(imm)     ((imm) & IMM_MASK)
 
 /* MIPS R-Type Instruction Format (Register-to-Register) */
 #define enc_r(op, rs, rt, rd, shamt, fc) (enc_op(op) | enc_rs(rs) | enc_rt(rt) | enc_rd(rd) | enc_shamt(shamt) | enc_fc(fc))