decode: make a real rotator instead of a loss

[firearm.git] / Decode.v

diff --git a/Decode.v b/Decode.v
index 44a948ca209ec22fe4137689bcc24b3e5c527009..cbe6184d5266a53e4a176a632e03dc7983b62461 100644 (file)
--- a/Decode.v
+++ b/Decode.v
@@ -26,6 +26,7 @@ module Decode(
        wire [31:0] shift_oper;
        wire [31:0] shift_res;
        wire shift_cflag_out;
+       wire [31:0] rotate_res;
 
        assign regs0 = (read_0 == 4'b1111) ? rpc : rdata_0;
        assign regs1 = (read_1 == 4'b1111) ? rpc : rdata_1;
@@ -38,6 +39,10 @@ module Decode(
                                   .res(shift_res),
                                   .cflag_out(shift_cflag_out));
 
+       SuckLessRotator whirr(.oper({24'b0, insn[7:0]}),
+                             .amt(insn[11:8]),
+                             .res(rotate_res));
+
        always @(*)
                casez (insn)
                32'b????000000??????????????1001????,   /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
@@ -152,7 +157,7 @@ module Decode(
                end
                 32'b????00?10?1010001111????????????: begin /* MSR (Transfer register or immediate to PSR, flag bits only) */
                        if(insn[25]) begin     /* the constant case */
-                               op0_out = ({24'b0, insn[7:0]} >> {insn[11:8], 1'b0}) | ({24'b0, insn[7:0]} << (5'b0 - {insn[11:8], 1'b0}));
+                               op0_out = rotate_res;
                        end else begin
                                op0_out = regs0;
                        end
@@ -161,7 +166,7 @@ module Decode(
                        op0_out = regs0;
                        if(insn[25]) begin     /* the constant case */
                                carry_out = incpsr[`CPSR_C];
-                               op1_out = ({24'b0, insn[7:0]} >> {insn[11:8], 1'b0}) | ({24'b0, insn[7:0]} << (5'b0 - {insn[11:8], 1'b0}));
+                               op1_out = rotate_res;
                        end else begin
                                carry_out = shift_cflag_out;
                                op1_out = shift_res;
@@ -317,3 +322,17 @@ module SuckLessShifter(
        assign {res, carryout} = amt[0] ? {is_rot ? stage5[0] : pushbits, stage5[31:1], stage5[0]} : stage5;
 
 endmodule
+
+module SuckLessRotator(
+       input [31:0] oper,
+       input [3:0] amt,
+       output [31:0] res
+);
+
+       wire [31:0] stage1, stage2, stage3;
+       assign stage1 = amt[3] ? {oper[15:0], oper[31:16]} : oper;
+       assign stage2 = amt[2] ? {stage1[7:0], stage1[31:8]} : stage1;
+       assign stage3 = amt[1] ? {stage2[3:0], stage2[31:4]} : stage2;
+       assign res    = amt[0] ? {stage3[1:0], stage3[31:2]} : stage3;
+
+endmodule