From 8e346d1477c1c1e8b7f20217a4c277bf0411fc4a Mon Sep 17 00:00:00 2001
From: Ryan Oldenburg <ryan@guzba.com>
Date: Sun, 17 Oct 2021 22:33:53 -0500
Subject: [PATCH] simd magnifyBy2 faster still

---
 src/pixie/images.nim | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/src/pixie/images.nim b/src/pixie/images.nim
index 6b60b7e..d9c5a86 100644
--- a/src/pixie/images.nim
+++ b/src/pixie/images.nim
@@ -331,12 +331,29 @@ proc magnifyBy2*(image: Image, power = 1): Image {.raises: [PixieError].} =
 
   for y in 0 ..< image.height:
     # Write one row of pixels duplicated by scale
-    for x in 0 ..< image.width:
+    var x: int
+    when defined(amd64) and not defined(pixieNoSimd):
+      if scale == 2:
+        let mask = cast[M128i]([uint32.high, 0, 0, 0])
+        for _ in countup(0, image.width - 4, 2):
+          let
+            values = mm_loadu_si128(image.data[image.dataIndex(x, y)].addr)
+            first = mm_and_si128(values, mask)
+            second = mm_and_si128(mm_srli_si128(values, 4), mask)
+            combined = mm_or_si128(first, mm_slli_si128(second, 8))
+            doubled = mm_or_si128(combined, mm_slli_si128(combined, 4))
+          mm_storeu_si128(
+            result.data[result.dataIndex(x * scale, y * scale)].addr,
+            doubled
+          )
+          x += 2
+    for _ in x ..< image.width:
       let
         rgbx = image.getRgbaUnsafe(x, y)
-        idx = result.dataIndex(x * scale, y * scale)
+        resultIdx = result.dataIndex(x * scale, y * scale)
       for i in 0 ..< scale:
-        result.data[idx + i] = rgbx
+        result.data[resultIdx + i] = rgbx
+      inc x
     # Copy that row of pixels into (scale - 1) more rows
     let rowStart = result.dataIndex(0, y * scale)
     for i in 1 ..< scale: