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[firearm.git] / Decode.v
diff --git a/Decode.v b/Decode.v
index 506480d81de2934d28c551379263e46cdc140007..7accb9d4c130735f2b99ea5277248eab6f508738 100644 (file)
--- a/Decode.v
+++ b/Decode.v
@@ -2,250 +2,350 @@
 
 module Decode(
        input clk,
 
 module Decode(
        input clk,
-       input [31:0] insn,
-       input [31:0] inpc,
+       input stall,
+       input [31:0] insn_1a,
+       input [31:0] pc_1a,
        input [31:0] incpsr,
        input [31:0] incpsr,
+       input [31:0] inspsr,
        output reg [31:0] op0,
        output reg [31:0] op1,
        output reg [31:0] op2,
        output reg [31:0] op0,
        output reg [31:0] op1,
        output reg [31:0] op2,
+       output reg carry,
        output reg [31:0] outcpsr,
        output reg [31:0] outcpsr,
+       output reg [31:0] outspsr,
 
 
-       output [3:0] read_0,
-       output [3:0] read_1,
-       output [3:0] read_2,
-       input [31:0] rdata_0,
-       input [31:0] rdata_1,
-       input [31:0] rdata_2
+       output reg [3:0] rf__read_0_1a,
+       output reg [3:0] rf__read_1_1a,
+       output reg [3:0] rf__read_2_1a,
+       input [31:0] rf__rdata_0_1a,
+       input [31:0] rf__rdata_1_1a,
+       input [31:0] rf__rdata_2_1a
        );
 
        );
 
-       wire [31:0] regs0, regs1, regs2, rpc;
-       wire [31:0] op1_res, cpsr;
+       wire [31:0] regs0, regs1, regs2;
+       reg [31:0] rpc;
+       reg [31:0] op0_out, op1_out, op2_out;
+       reg carry_out;
 
        /* shifter stuff */
        wire [31:0] shift_oper;
        wire [31:0] shift_res;
        wire shift_cflag_out;
 
        /* shifter stuff */
        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;
-       assign regs2 = rdata_2; /* use regs2 for things that cannot be r15 */
+       assign regs0 = (rf__read_0_1a == 4'b1111) ? rpc : rf__rdata_0_1a;
+       assign regs1 = (rf__read_1_1a == 4'b1111) ? rpc : rf__rdata_1_1a;
+       assign regs2 = rf__rdata_2_1a; /* use regs2 for things that cannot be r15 */
+
+       IREALLYHATEARMSHIFT shift(.insn(insn_1a),
+                                 .operand(regs1),
+                                 .reg_amt(regs2),
+                                 .cflag_in(incpsr[`CPSR_C]),
+                                 .res(shift_res),
+                                 .cflag_out(shift_cflag_out));
+
+       SuckLessRotator whirr(.oper({24'b0, insn_1a[7:0]}),
+                             .amt(insn_1a[11:8]),
+                             .res(rotate_res));
 
 
-       IHATEARMSHIFT blowme(.insn(insn),
-                            .operand(regs1),
-                            .reg_amt(regs2),
-                            .cflag_in(incpsr[`CPSR_C]),
-                            .res(shift_res),
-                            .cflag_out(shift_cflag_out));
-       
        always @(*)
        always @(*)
-               casez (insn)
-               32'b????000000??????????????1001????,   /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
-//             32'b????00001???????????????1001????,   /* Multiply long */
-               32'b????00010?001111????000000000000,   /* MRS (Transfer PSR to register) */
-               32'b????00010?101001111100000000????,   /* MSR (Transfer register to PSR) */
-               32'b????00?10?1010001111????????????,   /* MSR (Transfer register or immediate to PSR, flag bits only) */
-               32'b????00010?00????????00001001????,   /* Atomic swap */
-               32'b????000100101111111111110001????,   /* Branch and exchange */
-               32'b????000??0??????????00001??1????,   /* Halfword transfer - register offset */
-               32'b????000??1??????????00001??1????,   /* Halfword transfer - register offset */
-               32'b????011????????????????????1????,   /* Undefined. I hate ARM */
-               32'b????01??????????????????????????,   /* Single data transfer */
-               32'b????100?????????????????????????,   /* Block data transfer */
-               32'b????101?????????????????????????,   /* Branch */
-               32'b????110?????????????????????????,   /* Coprocessor data transfer */
-               32'b????1110???????????????????0????,   /* Coprocessor data op */
-               32'b????1110???????????????????1????,   /* Coprocessor register transfer */
-               32'b????1111????????????????????????:   /* SWI */
-                       rpc = inpc - 8;
-               32'b????00??????????????????????????:   /* ALU */
-                       rpc = inpc - (insn[25] ? 8 : (insn[4] ? 12 : 8));
-               default:                                /* X everything else out */
+               casez (insn_1a)
+               `DECODE_ALU_MULT,               /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
+//             `DECODE_ALU_MUL_LONG,           /* Multiply long */
+               `DECODE_ALU_MRS,                /* MRS (Transfer PSR to register) */
+               `DECODE_ALU_MSR,                /* MSR (Transfer register to PSR) */
+               `DECODE_ALU_MSR_FLAGS,          /* MSR (Transfer register or immediate to PSR, flag bits only) */
+               `DECODE_ALU_SWP,                /* Atomic swap */
+               `DECODE_ALU_BX,                 /* Branch and exchange */
+               `DECODE_ALU_HDATA_REG,          /* Halfword transfer - register offset */
+               `DECODE_ALU_HDATA_IMM,          /* Halfword transfer - register offset */
+               `DECODE_LDRSTR_UNDEFINED,       /* Undefined. I hate ARM */
+               `DECODE_LDRSTR,                 /* Single data transfer */
+               `DECODE_LDMSTM,                 /* Block data transfer */
+               `DECODE_BRANCH,                 /* Branch */
+               `DECODE_LDCSTC,                 /* Coprocessor data transfer */
+               `DECODE_CDP,                    /* Coprocessor data op */
+               `DECODE_SWI:                    /* SWI */
+                       rpc = pc_1a + 8;
+               `DECODE_MRCMCR:                 /* Coprocessor register transfer */
+                       rpc = pc_1a + 12;
+               `DECODE_ALU:                    /* ALU */
+                       rpc = pc_1a + (insn_1a[25] ? 8 : (insn_1a[4] ? 12 : 8));
+               default:                        /* X everything else out */
                        rpc = 32'hxxxxxxxx;
                endcase
                        rpc = 32'hxxxxxxxx;
                endcase
-
-       always @(*)
-               casez (insn)
-               32'b????000000??????????????1001????:   /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
-                       read_0 = insn[15:12]; /* Rn */
-//             32'b????00001???????????????1001????,   /* Multiply long */
-//                     read_0 = insn[11:8]; /* Rn */
-               32'b????00010?001111????000000000000,   /* MRS (Transfer PSR to register) */
-               32'b????00010?101001111100000000????,   /* MSR (Transfer register to PSR) */
-               32'b????00?10?1010001111????????????:   /* MSR (Transfer register or immediate to PSR, flag bits only) */
-                       read_0 = 4'hx;
-               32'b????00??????????????????????????:   /* ALU */
-                       read_0 = insn[19:16]; /* Rn */
-               32'b????00010?00????????00001001????:   /* Atomic swap */
-                       read_0 = insn[19:16]; /* Rn */
-               32'b????000100101111111111110001????:   /* Branch and exchange */
-                       read_0 = insn[3:0];   /* Rn */
-               32'b????000??0??????????00001??1????:   /* Halfword transfer - register offset */
-                       read_0 = insn[19:16];
-               32'b????000??1??????????00001??1????:   /* Halfword transfer - register offset */
-                       read_0 = insn[19:16];
-               32'b????011????????????????????1????:   /* Undefined. I hate ARM */
-                       read_0 = 4'hx;
-               32'b????01??????????????????????????:   /* Single data transfer */
-                       read_0 = insn[19:16]; /* Rn */
-               32'b????100?????????????????????????:   /* Block data transfer */
-                       read_0 = insn[19:16];
-               32'b????101?????????????????????????:   /* Branch */
-                       read_0 = 4'hx;
-               32'b????110?????????????????????????:   /* Coprocessor data transfer */
-                       read_0 = insn[19:16];
-               32'b????1110???????????????????0????,   /* Coprocessor data op */
-               32'b????1110???????????????????1????,   /* Coprocessor register transfer */
-               32'b????1111????????????????????????:   /* SWI */
-                       read_0 = 4'hx;
+       
+       always @(*) begin
+               rf__read_0_1a = 4'hx;
+               rf__read_1_1a = 4'hx;
+               rf__read_2_1a = 4'hx;
+               
+               casez (insn_1a)
+               `DECODE_ALU_MULT:       /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
+               begin
+                       rf__read_0_1a = insn_1a[15:12]; /* Rn */
+                       rf__read_1_1a = insn_1a[3:0];   /* Rm */
+                       rf__read_2_1a = insn_1a[11:8];  /* Rs */
+               end
+               `DECODE_ALU_MRS:        /* MRS (Transfer PSR to register) */
+               begin end
+               `DECODE_ALU_MSR:        /* MSR (Transfer register to PSR) */
+                       rf__read_0_1a = insn_1a[3:0];   /* Rm */
+               `DECODE_ALU_MSR_FLAGS:  /* MSR (Transfer register or immediate to PSR, flag bits only) */
+                       rf__read_0_1a = insn_1a[3:0];   /* Rm */
+               `DECODE_ALU_SWP:        /* Atomic swap */
+               begin
+                       rf__read_0_1a = insn_1a[19:16]; /* Rn */
+                       rf__read_1_1a = insn_1a[3:0];   /* Rm */
+               end
+               `DECODE_ALU_BX:         /* Branch and exchange */
+                       rf__read_0_1a = insn_1a[3:0];   /* Rn */
+               `DECODE_ALU_HDATA_REG:  /* Halfword transfer - register offset */
+               begin
+                       rf__read_0_1a = insn_1a[19:16];
+                       rf__read_1_1a = insn_1a[3:0];
+                       rf__read_2_1a = insn_1a[15:12];
+               end
+               `DECODE_ALU_HDATA_IMM:  /* Halfword transfer - immediate offset */
+               begin
+                       rf__read_0_1a = insn_1a[19:16];
+                       rf__read_1_1a = insn_1a[15:12];
+               end
+               `DECODE_ALU:            /* ALU */
+               begin
+                       rf__read_0_1a = insn_1a[19:16]; /* Rn */
+                       rf__read_1_1a = insn_1a[3:0];   /* Rm */
+                       rf__read_2_1a = insn_1a[11:8];  /* Rs for shift */
+               end
+               `DECODE_LDRSTR_UNDEFINED:       /* Undefined. I hate ARM */
+               begin end
+               `DECODE_LDRSTR:         /* Single data transfer */
+               begin
+                       rf__read_0_1a = insn_1a[19:16]; /* Rn */
+                       rf__read_1_1a = insn_1a[3:0];   /* Rm */
+                       rf__read_2_1a = insn_1a[15:12];
+               end
+               `DECODE_LDMSTM:         /* Block data transfer */
+                       rf__read_0_1a = insn_1a[19:16];
+               `DECODE_BRANCH:         /* Branch */
+               begin end
+               `DECODE_LDCSTC:         /* Coprocessor data transfer */
+                       rf__read_0_1a = insn_1a[19:16];
+               `DECODE_CDP:            /* Coprocessor data op */
+               begin end
+               `DECODE_MRCMCR:         /* Coprocessor register transfer */
+                       rf__read_0_1a = insn_1a[15:12];
+               `DECODE_SWI:            /* SWI */
+               begin end
                default:
                default:
-                       read_0 = 4'hx;
+                       $display("Undecoded instruction");
                endcase
                endcase
-
-       always @ (*) begin
-               casez (insn)
-               32'b????000000??????????????1001????: begin /* Multiply */
-                       read_1 = insn[3:0];   /* Rm */
-                       read_2 = insn[11:8];  /* Rs */
-                       op1_res = regs1;
-                       cpsr = incpsr;
-               end
-/*             32'b????00001???????????????1001????: begin * Multiply long *
-                       
-                       read_1 = insn[3:0];  * Rm *
-                       read_2 = 4'b0;       * anyus *
-                       op1_res = regs1;
-               end*/
-               32'b????00010?001111????000000000000: begin /* MRS (Transfer PSR to register) */
-                       cpsr = incpsr;
-               end
-               32'b????00010?101001111100000000????: begin /* MSR (Transfer register to PSR) */
-                       cpsr = incpsr;
-               end
-                32'b????00?10?1010001111????????????: begin /* MSR (Transfer register or immediate to PSR, flag bits onry) */
-                       cpsr = incpsr;
-                end
-               32'b????00??????????????????????????: begin /* ALU */
-                       read_1 = insn[3:0];   /* Rm */
-                       read_2 = insn[11:8];  /* Rs for shift */
-                       if(insn[25]) begin     /* the constant case */
-                               cpsr = incpsr;
-                               op1_res = ({24'b0, insn[7:0]} >> {insn[11:8], 1'b0}) | ({24'b0, insn[7:0]} << (5'b0 - {insn[11:8], 1'b0}));
-                       end else begin
-                               cpsr = {incpsr[31:30], shift_cflag_out, incpsr[28:0]};
-                               op1_res = shift_res;
-                       end
+       end
+       
+       always @(*) begin
+               op0_out = 32'hxxxxxxxx;
+               op1_out = 32'hxxxxxxxx;
+               op2_out = 32'hxxxxxxxx;
+               carry_out = 1'bx;
+               
+               casez (insn_1a)
+               `DECODE_ALU_MULT:       /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
+               begin
+                       op0_out = regs0;
+                       op1_out = regs1;
+                       op2_out = regs2;
                end
                end
-               32'b????00010?00????????00001001????: begin /* Atomic swap */
-                       read_1 = insn[3:0];   /* Rm */
-                       read_2 = 4'b0;        /* anyus */
-                       op1_res = regs1;
-               end
-               32'b????000100101111111111110001????: begin /* Branch and exchange */
-                       cpsr = incpsr;
-               end
-               32'b????000??0??????????00001??1????: begin /* Halfword transfer - register offset */
-                       read_1 = insn[3:0];
-                       read_2 = 4'b0;
-                       op1_res = regs1;
-                       cpsr = incpsr;
-               end
-               32'b????000??1??????????00001??1????: begin /* Halfword transfer - immediate offset */
-                       
-                       read_1 = insn[3:0];
-                       op1_res = {24'b0, insn[11:8], insn[3:0]};
-                       cpsr = incpsr;
-               end
-               32'b????011????????????????????1????: begin /* Undefined. I hate ARM */
-                       /* eat shit */
-               end
-               32'b????01??????????????????????????: begin /* Single data transfer */
-                       read_1 = insn[3:0];   /* Rm */
-                       if(insn[25]) begin
-                               op1_res = {20'b0, insn[11:0]};
-                               cpsr = incpsr;
+               `DECODE_ALU_MRS:        /* MRS (Transfer PSR to register) */
+               begin end
+               `DECODE_ALU_MSR:        /* MSR (Transfer register to PSR) */
+                       op0_out = regs0;
+               `DECODE_ALU_MSR_FLAGS:  /* MSR (Transfer register or immediate to PSR, flag bits only) */
+                       if(insn_1a[25]) begin     /* the constant case */
+                               op0_out = rotate_res;
                        end else begin
                        end else begin
-                               op1_res = shift_res;
-                               cpsr = {incpsr[31:30], shift_cflag_out, incpsr[28:0]};
+                               op0_out = regs0;
                        end
                        end
+               `DECODE_ALU_SWP:        /* Atomic swap */
+               begin
+                       op0_out = regs0;
+                       op1_out = regs1;
                end
                end
-               32'b????100?????????????????????????: begin /* Block data transfer */
-                       op1_res = {16'b0, insn[15:0]};
-                       cpsr = incpsr;
+               `DECODE_ALU_BX:         /* Branch and exchange */
+                       op0_out = regs0;
+               `DECODE_ALU_HDATA_REG:  /* Halfword transfer - register offset */
+               begin
+                       op0_out = regs0;
+                       op1_out = regs1;
+                       op2_out = regs2;
                end
                end
-               32'b????101?????????????????????????: begin /* Branch */
-                       op1_res = {{6{insn[23]}}, insn[23:0], 2'b0};
-                       cpsr = incpsr;
+               `DECODE_ALU_HDATA_IMM:  /* Halfword transfer - immediate offset */
+               begin
+                       op0_out = regs0;
+                       op1_out = {24'b0, insn_1a[11:8], insn_1a[3:0]};
+                       op2_out = regs1;
                end
                end
-               32'b????110?????????????????????????: begin /* Coprocessor data transfer */
-                       op1_res = {24'b0, insn[7:0]};
-                       cpsr = incpsr;
+               `DECODE_ALU:            /* ALU */
+               begin
+                       op0_out = regs0;
+                       if(insn_1a[25]) begin     /* the constant case */
+                               carry_out = incpsr[`CPSR_C];
+                               op1_out = rotate_res;
+                       end else begin
+                               carry_out = shift_cflag_out;
+                               op1_out = shift_res;
+                       end
                end
                end
-               32'b????1110???????????????????0????: begin /* Coprocessor data op */
-                       cpsr = incpsr;
+               `DECODE_LDRSTR:         /* Single data transfer */
+               begin
+                       op0_out = regs0;
+                       if(!insn_1a[25] /* immediate */) begin
+                               op1_out = {20'b0, insn_1a[11:0]};
+                               carry_out = incpsr[`CPSR_C];
+                       end else begin
+                               op1_out = shift_res;
+                               carry_out = shift_cflag_out;
+                       end
+                       op2_out = regs2;
                end
                end
-               32'b????1110???????????????????1????: begin /* Coprocessor register transfer */
-                       cpsr = incpsr;
+               `DECODE_LDMSTM:         /* Block data transfer */
+               begin
+                       op0_out = regs0;
+                       op1_out = {16'b0, insn_1a[15:0]};
                end
                end
-               32'b????1111????????????????????????: begin /* SWI */
-                       cpsr = incpsr;
+               `DECODE_BRANCH:         /* Branch */
+                       op0_out = {{6{insn_1a[23]}}, insn_1a[23:0], 2'b0};
+               `DECODE_LDCSTC:         /* Coprocessor data transfer */
+               begin
+                       op0_out = regs0;
+                       op1_out = {24'b0, insn_1a[7:0]};
                end
                end
-               default: begin end
+               `DECODE_CDP:            /* Coprocessor data op */
+               begin end
+               `DECODE_MRCMCR:         /* Coprocessor register transfer */
+                       op0_out = regs0;
+               `DECODE_SWI:            /* SWI */
+               begin end
                endcase
        end
                endcase
        end
-
+       
        always @ (posedge clk) begin
        always @ (posedge clk) begin
-               op0 <= regs0;   /* Rn - always */
-               op1 <= op1_res; /* 'operand 2' - Rm */
-               op2 <= regs2;   /* thirdedge - Rs */
-               outcpsr <= cpsr;
+               if (!stall)
+               begin
+                       op0 <= op0_out;   /* Rn - always */
+                       op1 <= op1_out; /* 'operand 2' - Rm */
+                       op2 <= op2_out;   /* thirdedge - Rs */
+                       carry <= carry_out;
+                       outcpsr <= incpsr;
+                       outspsr <= inspsr;
+               end
        end
 
 endmodule
 
        end
 
 endmodule
 
-module IHATEARMSHIFT(
+module IREALLYHATEARMSHIFT(
        input [31:0] insn,
        input [31:0] operand,
        input [31:0] reg_amt,
        input cflag_in,
        input [31:0] insn,
        input [31:0] operand,
        input [31:0] reg_amt,
        input cflag_in,
-       output [31:0] res,
-       output cflag_out
+       output reg [31:0] res,
+       output reg cflag_out
 );
        wire [5:0] shift_amt;
 );
        wire [5:0] shift_amt;
-       wire elanus;
+       reg is_arith, is_rot;
+       wire rshift_cout;
+       wire [31:0] rshift_res;
+
+       assign shift_amt = insn[4] ? {|reg_amt[7:5], reg_amt[4:0]}     /* reg-specified shift */
+                                  : {insn[11:7] == 5'b0, insn[11:7]}; /* immediate shift */
 
 
+       SuckLessShifter barrel(.oper(operand),
+                              .carryin(cflag_in),
+                              .amt(shift_amt),
+                              .is_arith(is_arith),
+                              .is_rot(is_rot),
+                              .res(rshift_res),
+                              .carryout(rshift_cout));
 
 
-       /* might want to write our own damn shifter that does arithmetic/logical efficiently and stuff */
        always @(*)
        always @(*)
-               if(insn[4]) begin
-                       shift_amt = {|reg_amt[7:5], reg_amt[4:0]};
-                       elanus = 1'b1;
-               end else begin
-                       shift_amt = {insn[11:7] == 5'b0, insn[11:7]};
-                       elanus = 1'b0;
+               case (insn[6:5])
+               `SHIFT_LSL: begin
+                       /* meaningless */
+                       is_rot = 1'b0;
+                       is_arith = 1'b0;
                end
                end
-       
+               `SHIFT_LSR: begin
+                       is_rot = 1'b0;
+                       is_arith = 1'b0;
+               end
+               `SHIFT_ASR: begin
+                       is_rot = 1'b0;
+                       is_arith = 1'b1;
+               end
+               `SHIFT_ROR: begin
+                       is_rot = 1'b1;
+                       is_arith = 1'b0;
+               end
+               endcase
+
        always @(*)
                case (insn[6:5]) /* shift type */
        always @(*)
                case (insn[6:5]) /* shift type */
-               `SHIFT_LSL: begin
-                       {cflag_out, res} = {cflag_in, operand} << {elanus & shift_amt[5], shift_amt[4:0]};
-               end
+               `SHIFT_LSL:
+                       {cflag_out, res} = {cflag_in, operand} << {insn[4] & shift_amt[5], shift_amt[4:0]};
                `SHIFT_LSR: begin
                `SHIFT_LSR: begin
-                       {res, cflag_out} = {operand, cflag_in} >> shift_amt;
+                       res = rshift_res;
+                       cflag_out = rshift_cout;
                end
                `SHIFT_ASR: begin
                end
                `SHIFT_ASR: begin
-                       {res, cflag_out} = {operand, cflag_in} >> shift_amt | (operand[31] ? ~(33'h1FFFFFFFF >> shift_amt) : 33'b0);
+                       res = rshift_res;
+                       cflag_out = rshift_cout;
                end
                `SHIFT_ROR: begin
                end
                `SHIFT_ROR: begin
-                       if(!elanus && shift_amt[4:0] == 5'b0) begin /* RRX x.x */
+                       if(!insn[4] && shift_amt[4:0] == 5'b0) begin /* RRX x.x */
                                res = {cflag_in, operand[31:1]};
                                cflag_out = operand[0];
                                res = {cflag_in, operand[31:1]};
                                cflag_out = operand[0];
-                       end else if(shift_amt == 6'b0) begin
-                               res = operand;
-                               cflag_out = cflag_in;
                        end else begin
                        end else begin
-                               res = operand >> shift_amt[4:0] | operand << (5'b0 - shift_amt[4:0]);
-                               cflag_out = operand[shift_amt[4:0] - 5'b1];
+                               res = rshift_res;
+                               cflag_out = rshift_cout;
                        end
                end
                endcase
 endmodule
                        end
                end
                endcase
 endmodule
+
+module SuckLessShifter(
+       input [31:0] oper,
+       input carryin,
+       input [5:0] amt,
+       input is_arith,
+       input is_rot,
+       output wire [31:0] res,
+       output wire carryout
+);
+
+       wire [32:0] stage1, stage2, stage3, stage4, stage5;
+
+       wire pushbits = is_arith & oper[31];
+
+       /* do a barrel shift */
+       assign stage1 = amt[5] ? {is_rot ? oper : {32{pushbits}}, oper[31]} : {oper, carryin};
+       assign stage2 = amt[4] ? {is_rot ? stage1[16:1] : {16{pushbits}}, stage1[32:17], stage1[16]} : stage1;
+       assign stage3 = amt[3] ? {is_rot ? stage2[8:1] : {8{pushbits}}, stage2[32:9], stage2[8]} : stage2;
+       assign stage4 = amt[2] ? {is_rot ? stage3[4:1] : {4{pushbits}}, stage3[32:5], stage3[4]} : stage3;
+       assign stage5 = amt[1] ? {is_rot ? stage4[2:1] : {2{pushbits}}, stage4[32:3], stage4[2]} : stage4;
+       assign {res, carryout} = amt[0] ? {is_rot ? stage5[1] : pushbits, stage5[32:2], stage5[1]} : stage5;
+
+endmodule
+
+module SuckLessRotator(
+       input [31:0] oper,
+       input [3:0] amt,
+       output wire [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
+
FireARM pipelined ARM-like CPU implementation in Verilog
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