From 623dbb73df7d8350f79f62c13587a354fdcd56d5 Mon Sep 17 00:00:00 2001
From: SamTebbs33 <samuel.tebbs@gmail.com>
Date: Thu, 27 Jun 2019 22:23:09 +0100
Subject: [PATCH] Add check for power of 2 to std.mem.alignBackward

---
 std/mem.zig | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/std/mem.zig b/std/mem.zig
index 969b9af4c1..ef001d5dab 100644
--- a/std/mem.zig
+++ b/std/mem.zig
@@ -1481,7 +1481,7 @@ test "subArrayPtr" {
 }
 
 /// Round an address up to the nearest aligned address
-/// The alignment must be greater than 0.
+/// The alignment must be a power of 2 and greater than 0.
 pub fn alignForward(addr: usize, alignment: usize) usize {
     return alignBackward(addr + (alignment - 1), alignment);
 }
@@ -1502,8 +1502,9 @@ test "alignForward" {
 }
 
 /// Round an address up to the previous aligned address
-/// The alignment must be greater than 0.
+/// The alignment must be a power of 2 and greater than 0.
 pub fn alignBackward(addr: usize, alignment: usize) usize {
+    assert(@popCount(usize, alignment) == 1);
     // 000010000 // example addr
     // 000001111 // subtract 1
     // 111110000 // binary not
@@ -1511,7 +1512,7 @@ pub fn alignBackward(addr: usize, alignment: usize) usize {
 }
 
 /// Given an address and an alignment, return true if the address is a multiple of the alignment
-/// The alignment must be greater than 0.
+/// The alignment must be a power of 2 and greater than 0.
 pub fn isAligned(addr: usize, alignment: usize) bool {
     return alignBackward(addr, alignment) == addr;
 }