diff --git a/.gitignore b/.gitignore
index 8738c93..08982ca 100644
--- a/.gitignore
+++ b/.gitignore
@@ -28,3 +28,4 @@ out/**
 !out/.gitkeep
 build/**
 !build/.gitkeep
+.DS_Store
diff --git a/src/ext/b/zbs.sv b/src/ext/b/zbs.sv
new file mode 100644
index 0000000..e0d8c9f
--- /dev/null
+++ b/src/ext/b/zbs.sv
@@ -0,0 +1,49 @@
+// -----------------------------------------------------------------------------
+// Zbs Extension – Single-Bit Instructions (RV32)
+// Reference:
+//   RISC-V Bitmanip Extension Specification v1.0.0
+//   Section 5.4 – Zbs (Single-Bit Instructions)
+//
+// Notes:
+//   - Purely combinational logic
+//   - Bit index = reg2[4:0]
+//   - R/I distinction handled in decode stage
+// -----------------------------------------------------------------------------
+
+module zbs (
+    input  data_t reg1 // rs1 operand
+  , input  data_t reg2 // rs2 or immediate (bit index source)
+  , input  logic [1:0] inst // operation selector
+  , output data_t out //result
+);
+
+    logic [4:0] index;
+    data_t mask;
+
+    always_comb
+        index = reg2[4:0];
+
+    always_comb
+        mask = data_t'(32'h1) << index;
+
+    always_comb
+        case (inst)
+
+            // 00 : bclr / bclri  → clear selected bit
+            2'b00: out = reg1 & ~mask;
+
+            // 01 : bset / bseti  → set selected bit
+            2'b01: out = reg1 | mask;
+
+            // 10 : binv / binvi  → invert selected bit
+            2'b10: out = reg1 ^ mask;
+
+            // 11 : bext / bexti  → extract selected bit (to bit[0])
+            2'b11: out = (reg1 >> index) & data_t'(32'h1);
+
+            // others → safe default
+            default: out = '0;
+
+        endcase
+
+endmodule
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