fix: improve perf of instructions w/ rotr

src/cpu/arm/half_signed_data_transfer.zig

@@ -5,6 +5,7 @@ const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
 const InstrFn = @import("../../cpu.zig").ArmInstrFn;
 
 const sext = @import("../../util.zig").sext;
+const rotr = @import("../../util.zig").rotr;
 
 pub fn halfAndSignedDataTransfer(comptime P: bool, comptime U: bool, comptime I: bool, comptime W: bool, comptime L: bool) InstrFn {
     return struct {
@@ -38,7 +39,7 @@ pub fn halfAndSignedDataTransfer(comptime P: bool, comptime U: bool, comptime I:
                     0b01 => {
                         // LDRH
                         const value = bus.read16(address & 0xFFFF_FFFE);
-                        result = std.math.rotr(u32, value, 8 * (address & 1));
+                        result = rotr(u32, value, 8 * (address & 1));
                     },
                     0b10 => {
                         // LDRSB
@@ -52,7 +53,7 @@ pub fn halfAndSignedDataTransfer(comptime P: bool, comptime U: bool, comptime I:
                             break :blk sext(16, bus.read16(address));
                         };
 
-                        result = std.math.rotr(u32, value, 8 * (address & 1));
+                        result = rotr(u32, value, 8 * (address & 1));
                     },
                     0b00 => unreachable, // SWP
                 }

src/cpu/arm/psr_transfer.zig

@@ -7,6 +7,8 @@ const PSR = @import("../../cpu.zig").PSR;
 
 const log = std.log.scoped(.PsrTransfer);
 
+const rotr = @import("../../util.zig").rotr;
+
 pub fn psrTransfer(comptime I: bool, comptime R: bool, comptime kind: u2) InstrFn {
     return struct {
         fn inner(cpu: *Arm7tdmi, _: *Bus, opcode: u32) void {
@@ -22,7 +24,7 @@ pub fn psrTransfer(comptime I: bool, comptime R: bool, comptime kind: u2) InstrF
                     // MSR
                     const field_mask = @truncate(u4, opcode >> 16 & 0xF);
                     const rm_idx = opcode & 0xF;
-                    const right = if (I) std.math.rotr(u32, opcode & 0xFF, (opcode >> 8 & 0xF) << 1) else cpu.r[rm_idx];
+                    const right = if (I) rotr(u32, opcode & 0xFF, (opcode >> 8 & 0xF) << 1) else cpu.r[rm_idx];
 
                     if (R and !cpu.hasSPSR()) log.warn("Tried to write to SPSR in User/System Mode", .{});
 

src/cpu/arm/single_data_swap.zig

@@ -4,6 +4,8 @@ const Bus = @import("../../Bus.zig");
 const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
 const InstrFn = @import("../../cpu.zig").ArmInstrFn;
 
+const rotr = @import("../../util.zig").rotr;
+
 pub fn singleDataSwap(comptime B: bool) InstrFn {
     return struct {
         fn inner(cpu: *Arm7tdmi, bus: *Bus, opcode: u32) void {
@@ -20,7 +22,7 @@ pub fn singleDataSwap(comptime B: bool) InstrFn {
                 cpu.r[rd] = value;
             } else {
                 // SWP
-                const value = std.math.rotr(u32, bus.read32(address & 0xFFFF_FFFC), 8 * (address & 0x3));
+                const value = rotr(u32, bus.read32(address & 0xFFFF_FFFC), 8 * (address & 0x3));
                 bus.write32(address & 0xFFFF_FFFC, cpu.r[rm]);
                 cpu.r[rd] = value;
             }

src/cpu/arm/single_data_transfer.zig

@@ -6,6 +6,8 @@ const Bus = @import("../../Bus.zig");
 const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
 const InstrFn = @import("../../cpu.zig").ArmInstrFn;
 
+const rotr = @import("../../util.zig").rotr;
+
 pub fn singleDataTransfer(comptime I: bool, comptime P: bool, comptime U: bool, comptime B: bool, comptime W: bool, comptime L: bool) InstrFn {
     return struct {
         fn inner(cpu: *Arm7tdmi, bus: *Bus, opcode: u32) void {
@@ -33,7 +35,7 @@ pub fn singleDataTransfer(comptime I: bool, comptime P: bool, comptime U: bool,
                 } else {
                     // LDR
                     const value = bus.read32(address & 0xFFFF_FFFC);
-                    result = std.math.rotr(u32, value, 8 * (address & 0x3));
+                    result = rotr(u32, value, 8 * (address & 0x3));
                 }
             } else {
                 if (B) {

src/cpu/barrel_shifter.zig

@@ -3,6 +3,8 @@ const std = @import("std");
 const Arm7tdmi = @import("../cpu.zig").Arm7tdmi;
 const CPSR = @import("../cpu.zig").PSR;
 
+const rotr = @import("../util.zig").rotr;
+
 pub fn execute(comptime S: bool, cpu: *Arm7tdmi, opcode: u32) u32 {
     var result: u32 = undefined;
     if (opcode >> 4 & 1 == 1) {
@@ -141,7 +143,7 @@ pub fn arithmeticRight(comptime S: bool, cpsr: *CPSR, rm: u32, total_amount: u8)
 }
 
 pub fn rotateRight(comptime S: bool, cpsr: *CPSR, rm: u32, total_amount: u8) u32 {
-    const result = std.math.rotr(u32, rm, total_amount);
+    const result = rotr(u32, rm, total_amount);
 
     if (S and total_amount != 0) {
         cpsr.c.write(result >> 31 & 1 == 1);

src/cpu/thumb/data_transfer.zig

@@ -4,6 +4,8 @@ const Bus = @import("../../Bus.zig");
 const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
 const InstrFn = @import("../../cpu.zig").ThumbInstrFn;
 
+const rotr = @import("../../util.zig").rotr;
+
 pub fn format6(comptime rd: u3) InstrFn {
     return struct {
         fn inner(cpu: *Arm7tdmi, bus: *Bus, opcode: u16) void {
@@ -39,7 +41,7 @@ pub fn format78(comptime op: u2, comptime T: bool) InstrFn {
                     0b10 => {
                         // LDRH
                         const value = bus.read16(address & 0xFFFF_FFFE);
-                        cpu.r[rd] = std.math.rotr(u32, value, 8 * (address & 1));
+                        cpu.r[rd] = rotr(u32, value, 8 * (address & 1));
                     },
                     0b11 => {
                         // LDRSH
@@ -49,7 +51,7 @@ pub fn format78(comptime op: u2, comptime T: bool) InstrFn {
                             break :blk sext(16, bus.read16(address));
                         };
 
-                        cpu.r[rd] = std.math.rotr(u32, value, 8 * (address & 1));
+                        cpu.r[rd] = rotr(u32, value, 8 * (address & 1));
                     },
                 }
             } else {
@@ -66,7 +68,7 @@ pub fn format78(comptime op: u2, comptime T: bool) InstrFn {
                     0b10 => {
                         // LDR
                         const value = bus.read32(address & 0xFFFF_FFFC);
-                        cpu.r[rd] = std.math.rotr(u32, value, 8 * (address & 0x3));
+                        cpu.r[rd] = rotr(u32, value, 8 * (address & 0x3));
                     },
                     0b11 => {
                         // LDRB
@@ -93,7 +95,7 @@ pub fn format9(comptime B: bool, comptime L: bool, comptime offset: u5) InstrFn
                     // LDR
                     const address = cpu.r[rb] + (@as(u32, offset) << 2);
                     const value = bus.read32(address & 0xFFFF_FFFC);
-                    cpu.r[rd] = std.math.rotr(u32, value, 8 * (address & 0x3));
+                    cpu.r[rd] = rotr(u32, value, 8 * (address & 0x3));
                 }
             } else {
                 if (B) {
@@ -121,7 +123,7 @@ pub fn format10(comptime L: bool, comptime offset: u5) InstrFn {
             if (L) {
                 // LDRH
                 const value = bus.read16(address & 0xFFFF_FFFE);
-                cpu.r[rd] = std.math.rotr(u32, value, 8 * (address & 1));
+                cpu.r[rd] = rotr(u32, value, 8 * (address & 1));
             } else {
                 // STRH
                 bus.write16(address & 0xFFFF_FFFE, @truncate(u16, cpu.r[rd]));
@@ -139,7 +141,7 @@ pub fn format11(comptime L: bool, comptime rd: u3) InstrFn {
             if (L) {
                 // LDR
                 const value = bus.read32(address & 0xFFFF_FFFC);
-                cpu.r[rd] = std.math.rotr(u32, value, 8 * (address & 0x3));
+                cpu.r[rd] = rotr(u32, value, 8 * (address & 0x3));
             } else {
                 // STR
                 bus.write32(address & 0xFFFF_FFFC, cpu.r[rd]);

src/util.zig

@@ -1,12 +1,21 @@
 const std = @import("std");
+const Log2Int = std.math.Log2Int;
 
-pub fn sext(comptime bits: comptime_int, value: u32) u32 {
+pub inline fn sext(comptime bits: comptime_int, value: u32) u32 {
     comptime std.debug.assert(bits <= 32);
     const amount = 32 - bits;
 
     return @bitCast(u32, @bitCast(i32, value << amount) >> amount);
 }
 
+/// See https://godbolt.org/z/W3en9Eche
+pub inline fn rotr(comptime T: type, value: T, r: anytype) T {
+    comptime std.debug.assert(@typeInfo(T).Int.signedness == .unsigned);
+    const ar = @truncate(Log2Int(T), r);
+
+    return value >> ar | value << @truncate(Log2Int(T), @typeInfo(T).Int.bits - @as(T, ar));
+}
+
 pub const FpsAverage = struct {
     const Self = @This();