[FFmpeg-devel] [PATCH v2 2/7] avutil/half2float: adjust conversion of NaN

[Timo Rothenpieler]

IEEE-754 differentiates two different kind of NaNs.
Quiet and Signaling ones. They are differentiated by the MSB of the
mantissa.

For whatever reason, actual hardware conversion of half to single always
sets the signaling bit to 1 if the mantissa is != 0, and to 0 if it's 0.
So our code has to follow suite or fate-testing hardware float16 will be
impossible.
---
 libavcodec/exr.c                                    | 2 +-
 libavcodec/pnm.h                                    | 2 +-
 libavutil/half2float.h                              | 5 +++++
 tests/ref/fate/exr-rgb-scanline-zip-half-0x0-0xFFFF | 2 +-
 4 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/libavcodec/exr.c b/libavcodec/exr.c
index 5c6ca9adbf..47f4786491 100644
--- a/libavcodec/exr.c
+++ b/libavcodec/exr.c
@@ -191,7 +191,7 @@ typedef struct EXRContext {
     float gamma;
     union av_intfloat32 gamma_table[65536];
 
-    uint32_t mantissatable[2048];
+    uint32_t mantissatable[3072];
     uint32_t exponenttable[64];
     uint16_t offsettable[64];
 } EXRContext;
diff --git a/libavcodec/pnm.h b/libavcodec/pnm.h
index 5bf2eaa4d9..7e5445f529 100644
--- a/libavcodec/pnm.h
+++ b/libavcodec/pnm.h
@@ -34,7 +34,7 @@ typedef struct PNMContext {
     int half;
     float scale;
 
-    uint32_t mantissatable[2048];
+    uint32_t mantissatable[3072];
     uint32_t exponenttable[64];
     uint16_t offsettable[64];
 } PNMContext;
diff --git a/libavutil/half2float.h b/libavutil/half2float.h
index 1f6deade07..5af4690cfe 100644
--- a/libavutil/half2float.h
+++ b/libavutil/half2float.h
@@ -45,6 +45,9 @@ static void half2float_table(uint32_t *mantissatable, uint32_t *exponenttable,
         mantissatable[i] = convertmantissa(i);
     for (int i = 1024; i < 2048; i++)
         mantissatable[i] = 0x38000000UL + ((i - 1024) << 13UL);
+    for (int i = 2048; i < 3072; i++)
+        mantissatable[i] = mantissatable[i - 1024] | 0x400000UL;
+    mantissatable[2048] = mantissatable[1024];
 
     exponenttable[0] = 0;
     for (int i = 1; i < 31; i++)
@@ -58,7 +61,9 @@ static void half2float_table(uint32_t *mantissatable, uint32_t *exponenttable,
     offsettable[0] = 0;
     for (int i = 1; i < 64; i++)
         offsettable[i] = 1024;
+    offsettable[31] = 2048;
     offsettable[32] = 0;
+    offsettable[63] = 2048;
 }
 
 static uint32_t half2float(uint16_t h, const uint32_t *mantissatable, const uint32_t *exponenttable,
diff --git a/tests/ref/fate/exr-rgb-scanline-zip-half-0x0-0xFFFF b/tests/ref/fate/exr-rgb-scanline-zip-half-0x0-0xFFFF
index b6201116fe..e45a40b498 100644
--- a/tests/ref/fate/exr-rgb-scanline-zip-half-0x0-0xFFFF
+++ b/tests/ref/fate/exr-rgb-scanline-zip-half-0x0-0xFFFF
@@ -3,4 +3,4 @@
 #codec_id 0: rawvideo
 #dimensions 0: 256x256
 #sar 0: 1/1
-0,          0,          0,        1,   786432, 0x1445e411
+0,          0,          0,        1,   786432, 0xce9be2be
-- 
2.34.1