From 8c65c68b734b3a0711e8d0a7282d6c7d9def5ddf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Sat, 6 Mar 2021 22:05:40 +0100
Subject: [PATCH] =?UTF-8?q?sixel:=20get=20rid=20of=20an=20=E2=80=98imul?=
 =?UTF-8?q?=E2=80=99=20in=20sixel=5Fadd()?=
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By storing the current row’s byte offset into the backing image in the
terminal struct.

This replaces the ‘imul’ with a load, which can potentially be
slow. But, this data should already be in the cache.
---
 sixel.c    | 6 ++++--
 terminal.h | 1 +
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/sixel.c b/sixel.c
index 6e7002d0..e0d5933a 100644
--- a/sixel.c
+++ b/sixel.c
@@ -37,6 +37,7 @@ sixel_init(struct terminal *term)
 
     term->sixel.state = SIXEL_DECSIXEL;
     term->sixel.pos = (struct coord){0, 0};
+    term->sixel.row_byte_ofs = 0;
     term->sixel.color_idx = 0;
     term->sixel.max_col = 0;
     term->sixel.param = 0;
@@ -908,6 +909,7 @@ resize(struct terminal *term, int new_width, int new_height)
     term->sixel.image.data = new_data;
     term->sixel.image.width = new_width;
     term->sixel.image.height = new_height;
+    term->sixel.row_byte_ofs = term->sixel.pos.row * new_width;
 
     return true;
 }
@@ -931,8 +933,7 @@ sixel_add(struct terminal *term, uint32_t color, uint8_t sixel)
             return;
     }
 
-    size_t ofs = term->sixel.pos.row * term->sixel.image.width;
-    ofs += term->sixel.pos.col;
+    size_t ofs = term->sixel.row_byte_ofs + term->sixel.pos.col;
 
     for (int i = 0; i < 6; i++, sixel >>= 1) {
         if (sixel & 1)
@@ -978,6 +979,7 @@ decsixel(struct terminal *term, uint8_t c)
             term->sixel.max_col = term->sixel.pos.col;
         term->sixel.pos.row += 6;
         term->sixel.pos.col = 0;
+        term->sixel.row_byte_ofs += term->sixel.image.width * 6;
         break;
 
     case '?': case '@': case 'A': case 'B': case 'C': case 'D': case 'E':
diff --git a/terminal.h b/terminal.h
index e4e662fb..2a8bb6f9 100644
--- a/terminal.h
+++ b/terminal.h
@@ -521,6 +521,7 @@ struct terminal {
         } state;
 
         struct coord pos;    /* Current sixel coordinate */
+        size_t row_byte_ofs; /* Byte position into image, for current row */
         int color_idx;       /* Current palette index */
         int max_col;         /* Largest column index we've seen (aka the image width) */
         uint32_t *private_palette;   /* Private palette, used when private mode 1070 is enabled */