From 3cafbdc083914d3a921fb241625ca8b6ccae1297 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20B=C5=93sch?= <u@pkh.me>
Date: Tue, 27 Dec 2022 17:38:10 +0100
Subject: [PATCH] avfilter/palette: add lowbias32 hashing

---
 libavfilter/palette.c | 10 ++++++++++
 libavfilter/palette.h |  5 +++++
 2 files changed, 15 insertions(+)

diff --git a/libavfilter/palette.c b/libavfilter/palette.c
index e3a27fc51e..bba136408c 100644
--- a/libavfilter/palette.c
+++ b/libavfilter/palette.c
@@ -207,3 +207,13 @@ uint32_t ff_oklab_int_to_srgb_u8(struct Lab c)
 
     return r<<16 | g<<8 | b;
 }
+
+uint32_t ff_lowbias32(uint32_t x)
+{
+    x ^= x >> 16;
+    x *= 0x7feb352d;
+    x ^= x >> 15;
+    x *= 0x846ca68b;
+    x ^= x >> 16;
+    return x;
+}
diff --git a/libavfilter/palette.h b/libavfilter/palette.h
index 6839bf6fc6..d3acc854ba 100644
--- a/libavfilter/palette.h
+++ b/libavfilter/palette.h
@@ -55,4 +55,9 @@ struct Lab ff_srgb_u8_to_oklab_int(uint32_t srgb);
  */
 uint32_t ff_oklab_int_to_srgb_u8(struct Lab c);
 
+/*
+ * lowbias32 hashing from https://nullprogram.com/blog/2018/07/31/
+ */
+uint32_t ff_lowbias32(uint32_t x);
+
 #endif /* AVFILTER_PALETTE_H */