Rename blackBox, move it to std.mem.forceEval()

Author: jedisct1

lib/std/crypto/benchmark.zig

@@ -7,6 +7,7 @@
 
 const builtin = @import("builtin");
 const std = @import("std");
+const mem = std.mem;
 const time = std.time;
 const Timer = time.Timer;
 const crypto = std.crypto;
@@ -21,14 +22,6 @@ const Crypto = struct {
     name: []const u8,
 };
 
-fn blackBox(x: anytype) void {
-    asm volatile (""
-        :
-        : [x] "rm" (x)
-        : "memory"
-    );
-}
-
 const hashes = [_]Crypto{
     Crypto{ .ty = crypto.hash.Md5, .name = "md5" },
     Crypto{ .ty = crypto.hash.Sha1, .name = "sha1" },
@@ -54,7 +47,7 @@ pub fn benchmarkHash(comptime Hash: anytype, comptime bytes: comptime_int) !u64
     while (offset < bytes) : (offset += block.len) {
         h.update(block[0..]);
     }
-    blackBox(&h);
+    mem.forceEval(&h);
     const end = timer.read();
 
     const elapsed_s = @intToFloat(f64, end - start) / time.ns_per_s;
@@ -89,7 +82,7 @@ pub fn benchmarkMac(comptime Mac: anytype, comptime bytes: comptime_int) !u64 {
     const start = timer.lap();
     while (offset < bytes) : (offset += in.len) {
         Mac.create(mac[0..], in[0..], key[0..]);
-        blackBox(&mac);
+        mem.forceEval(&mac);
     }
     const end = timer.read();
 
@@ -116,7 +109,7 @@ pub fn benchmarkKeyExchange(comptime DhKeyExchange: anytype, comptime exchange_c
         var i: usize = 0;
         while (i < exchange_count) : (i += 1) {
             _ = DhKeyExchange.create(out[0..], out[0..], in[0..]);
-            blackBox(&out);
+            mem.forceEval(&out);
         }
     }
     const end = timer.read();
@@ -141,7 +134,7 @@ pub fn benchmarkSignature(comptime Signature: anytype, comptime signatures_count
         var i: usize = 0;
         while (i < signatures_count) : (i += 1) {
             const s = try Signature.sign(&msg, key_pair, null);
-            blackBox(&s);
+            mem.forceEval(&s);
         }
     }
     const end = timer.read();
@@ -177,7 +170,7 @@ pub fn benchmarkAead(comptime Aead: anytype, comptime bytes: comptime_int) !u64
         Aead.encrypt(in[0..], tag[0..], in[0..], &[_]u8{}, nonce, key);
         Aead.decrypt(in[0..], in[0..], tag, &[_]u8{}, nonce, key) catch unreachable;
     }
-    blackBox(&in);
+    mem.forceEval(&in);
     const end = timer.read();
 
     const elapsed_s = @intToFloat(f64, end - start) / time.ns_per_s;

lib/std/math.zig

@@ -5,6 +5,7 @@
 // and substantial portions of the software.
 const std = @import("std.zig");
 const assert = std.debug.assert;
+const mem = std.mem;
 const testing = std.testing;
 
 /// Euler's number (e)
@@ -108,34 +109,8 @@ pub fn approxEq(comptime T: type, x: T, y: T, epsilon: T) bool {
     return fabs(x - y) < epsilon;
 }
 
-// TODO: Hide the following in an internal module.
 pub fn forceEval(value: anytype) void {
-    const T = @TypeOf(value);
-    switch (T) {
-        f16 => {
-            var x: f16 = undefined;
-            const p = @ptrCast(*volatile f16, &x);
-            p.* = x;
-        },
-        f32 => {
-            var x: f32 = undefined;
-            const p = @ptrCast(*volatile f32, &x);
-            p.* = x;
-        },
-        f64 => {
-            var x: f64 = undefined;
-            const p = @ptrCast(*volatile f64, &x);
-            p.* = x;
-        },
-        f128 => {
-            var x: f128 = undefined;
-            const p = @ptrCast(*volatile f128, &x);
-            p.* = x;
-        },
-        else => {
-            @compileError("forceEval not implemented for " ++ @typeName(T));
-        },
-    }
+    mem.forceEval(value);
 }
 
 pub fn raiseInvalid() void {

lib/std/mem.zig

@@ -2158,6 +2158,17 @@ pub fn alignForwardGeneric(comptime T: type, addr: T, alignment: T) T {
     return alignBackwardGeneric(T, addr + (alignment - 1), alignment);
 }
 
+/// Force an evaluation of the expression; this tries to prevent
+/// the compiler from optimizing the computation away even if the
+/// result eventually gets discarded.
+pub fn forceEval(val: anytype) void {
+    asm volatile (""
+        :
+        : [val] "rm" (val)
+        : "memory"
+    );
+}
+
 test "alignForward" {
     testing.expect(alignForward(1, 1) == 1);
     testing.expect(alignForward(2, 1) == 2);