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[MODS/VM]: Explain magic values in f32_abs and f64_abs

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luccie 2025-08-12 14:34:51 +02:00
parent 20ee18b85e
commit f2fd7a3f1b
1 changed files with 6 additions and 0 deletions
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6
src/mods/vm.zig
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@ -831,9 +831,11 @@ pub const Runtime = struct {
try self.stack.append(.{ .i64 = @intCast(std.math.rotr(u64, b, a)) }); try self.stack.append(.{ .i64 = @intCast(std.math.rotr(u64, b, a)) });
}, },
// The value 0x7FFFFFFF here represents the bitmask that masks everything except for the IEEE754 32 bit precision sign bit
.f32_abs => { .f32_abs => {
try self.stack.append(.{ .f32 = @bitCast(@as(u32, @bitCast(self.stack.pop().?.f32)) & 0x7FFFFFFF) }); try self.stack.append(.{ .f32 = @bitCast(@as(u32, @bitCast(self.stack.pop().?.f32)) & 0x7FFFFFFF) });
}, },
// The value 0x80000000 here represents the bitmask that only masks the IEEE754 32 bit precision sign bit
.f32_neg => { .f32_neg => {
try self.stack.append(.{ .f32 = @bitCast(@as(u32, @bitCast(self.stack.pop().?.f32)) ^ 0x80000000) }); try self.stack.append(.{ .f32 = @bitCast(@as(u32, @bitCast(self.stack.pop().?.f32)) ^ 0x80000000) });
}, },
@ -885,15 +887,18 @@ pub const Runtime = struct {
const b = self.stack.pop().?.f32; const b = self.stack.pop().?.f32;
try self.stack.append(.{ .f32 = @max(a, b) }); try self.stack.append(.{ .f32 = @max(a, b) });
}, },
// See f32_abs and f32_neg for explainations behind these magic values
.f32_copysign => { .f32_copysign => {
const a = self.stack.pop().?.f32; const a = self.stack.pop().?.f32;
const b = self.stack.pop().?.f32; const b = self.stack.pop().?.f32;
try self.stack.append(.{ .f32 = @bitCast((@as(u32, @bitCast(b)) & 0x7FFFFFFF) | (@as(u32, @bitCast(a)) & 0x80000000)) }); try self.stack.append(.{ .f32 = @bitCast((@as(u32, @bitCast(b)) & 0x7FFFFFFF) | (@as(u32, @bitCast(a)) & 0x80000000)) });
}, },
// The value 0x7FFFFFFFFFFFFFFF here represents the bitmask that masks everything except for the IEEE754 64 bit precision sign bit
.f64_abs => { .f64_abs => {
try self.stack.append(.{ .f64 = @bitCast(@as(u64, @bitCast(self.stack.pop().?.f64)) & 0x7FFFFFFFFFFFFFFF) }); try self.stack.append(.{ .f64 = @bitCast(@as(u64, @bitCast(self.stack.pop().?.f64)) & 0x7FFFFFFFFFFFFFFF) });
}, },
// The value 0x8000000000000000 here represents the bitmask that only masks the IEEE754 64 bit precision sign bit
.f64_neg => { .f64_neg => {
try self.stack.append(.{ .f64 = @bitCast(@as(u64, @bitCast(self.stack.pop().?.f64)) ^ 0x8000000000000000) }); try self.stack.append(.{ .f64 = @bitCast(@as(u64, @bitCast(self.stack.pop().?.f64)) ^ 0x8000000000000000) });
}, },
@ -942,6 +947,7 @@ pub const Runtime = struct {
const b = self.stack.pop().?.f64; const b = self.stack.pop().?.f64;
try self.stack.append(.{ .f64 = @max(a, b) }); try self.stack.append(.{ .f64 = @max(a, b) });
}, },
// See f64_abs and f64_neg for explainations behind these magic values
.f64_copysign => { .f64_copysign => {
const a = self.stack.pop().?.f64; const a = self.stack.pop().?.f64;
const b = self.stack.pop().?.f64; const b = self.stack.pop().?.f64;