Re: [FFmpeg-devel] [PATCH 06/11] avutil/half2float: adjust conversion of NaN

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

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.

What does the exr spec say about quiet and signaling nans?

> ---
>  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

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