diff --git a/fft.c b/fft.c
index f0d495b..9d1550f 100644
--- a/fft.c
+++ b/fft.c
@@ -60,14 +60,11 @@ int fix_fft(fixed fr[], fixed fi[], int m, int inverse)
     nn = n - 1;
     scale = 0;
     
+    int mm = m;
 
     /* decimation in time - re-order data */
     for(m=1; m<=nn; ++m) {
-        l = n;
-        do{
-        	l >>= 1;
-        }while(mr+l > nn);
-        mr = (mr & (l-1)) + l;
+        mr = FFT_bit_reverse(m, mm);
 
         if(mr <= m) continue;
         tr = fr[m];
@@ -119,23 +116,16 @@ int fix_fft(fixed fr[], fixed fi[], int m, int inverse)
         for(m=0; m<l; ++m)
         {
             j = m << k;
-            /* 0 <= j < N_WAVE/2 */
-            wr =  Sinewave[j+N_WAVE/4];
-            wi = -Sinewave[j];
-
-            if(inverse) wi = -wi;
-            if(shift)
-            {
-                wr >>= 1;
-                wi >>= 1;
-            }
+            
+            FFT_twiddle(wr, wi, j, shift, inverse);
+            
+            FFT_reg reg;
+            fixed *reg_s = ((fixed*) &reg);
+            
             for(i=m; i<n; i+=istep)
             {
                 j = i + l;
                 
-                FFT_reg reg;
-                fixed *reg_s = ((fixed*) &reg);
-                
                 reg_s[3] = fr[i];
                 reg_s[2] = fr[j];
                 reg_s[1] = fi[i];
diff --git a/fft_inst.tie b/fft_inst.tie
index 5748d72..05ce3a6 100644
--- a/fft_inst.tie
+++ b/fft_inst.tie
@@ -132,6 +132,31 @@ table SIN_wave 16 1024 {
 
 regfile FFT_reg 64 2 fftv
 
+operation FFT_bit_reverse {in AR b, out AR o, in AR m} {}
+{
+	assign o = {
+		TIEmux(m[2:0], 1'b0, 1'b0, 1'b0, 1'b0, 1'b0, 1'b0, 1'b0, b[0]),
+		TIEmux(m[2:0], 1'b0, 1'b0, 1'b0, 1'b0, 1'b0, 1'b0, b[0], b[1]),
+		TIEmux(m[2:0], 1'b0, 1'b0, 1'b0, 1'b0, 1'b0, b[0], b[1], b[2]),
+		TIEmux(m[2:0], 1'b0, 1'b0, 1'b0, 1'b0, b[0], b[1], b[2], b[3]),
+		TIEmux(m[2:0], 1'b0, 1'b0, 1'b0, b[0], b[1], b[2], b[3], b[4]),
+		TIEmux(m[2:0], 1'b0, 1'b0, b[0], b[1], b[2], b[3], b[4], b[5]),
+		TIEmux(m[2:0], 1'b0, b[0], b[1], b[2], b[3], b[4], b[5], b[6])
+	};
+}
+
+operation FFT_twiddle {out AR wr, out AR wi, in AR j, in BR shift, in BR inverse} {}
+{
+	// 256 = N_WAVE / 4
+	wire [9:0] idx = TIEadd(j, 256, 1'b0);
+	wire [15:0] sin = SIN_wave[j];
+	wire [15:0] wr1 = SIN_wave[idx];
+	wire [15:0] wi1 = TIEadd(~sin, 16'b0, 1'b1);
+	wire [15:0] wi2 = TIEmux(inverse, wi1, sin);
+	assign wr = TIEmux(shift, wr1, {wr1[15], wr1[15:1]});
+	assign wi = TIEmux(shift, wi2, {wi2[15], wi2[15:1]});
+}
+
 operation FFT_calc {inout FFT_reg data, in AR wr, in AR wi, in AR shift} {}
 {
 	wire [15:0] fri = data[63:48];
diff --git a/main.c b/main.c
index e958655..2503da1 100644
--- a/main.c
+++ b/main.c
@@ -73,6 +73,7 @@ int main()
         imag_org[i] = 0;
     }
 
+    /*
     //FFT
     fix_fft(real, imag, M, 0);
     fix_fft_org(real_org, imag_org, M, 0);
@@ -86,6 +87,7 @@ int main()
 
     printf("\nIFFT2\n");
     show_result(real, real_org, imag, imag_org, N);
+    */
 
     return 0;
 }