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[79.124.17.100]) by mx.google.com with ESMTP id x4-20020a05640226c400b0043a944f4458si13715485edd.573.2022.08.10.15.52.15; Wed, 10 Aug 2022 15:52:26 -0700 (PDT) Received-SPF: pass (google.com: domain of ffmpeg-devel-bounces@ffmpeg.org designates 79.124.17.100 as permitted sender) client-ip=79.124.17.100; Authentication-Results: mx.google.com; dkim=neutral (body hash did not verify) header.i=@rothenpieler.org header.s=mail header.b="sgtQ9Q/P"; spf=pass (google.com: domain of ffmpeg-devel-bounces@ffmpeg.org designates 79.124.17.100 as permitted sender) smtp.mailfrom=ffmpeg-devel-bounces@ffmpeg.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=rothenpieler.org Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id CF53A68B8D2; Thu, 11 Aug 2022 01:52:12 +0300 (EEST) X-Original-To: ffmpeg-devel@ffmpeg.org Delivered-To: ffmpeg-devel@ffmpeg.org Received: from btbn.de (btbn.de [136.243.74.85]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id B2F2E68B2D8 for ; Thu, 11 Aug 2022 01:52:06 +0300 (EEST) Received: from [authenticated] by btbn.de (Postfix) with ESMTPSA id 55CE22F6AA6; Thu, 11 Aug 2022 00:52:06 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rothenpieler.org; s=mail; t=1660171926; bh=m0QJxlHIYlA4ckm7ZgCwGvv5pep/CiEkHke24wkvzrk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=sgtQ9Q/PlsU0VfS3pTpShuO+C127Fk5AY6pX0fLAAhTC9LuSPUpOtzJY4OZvd3uBB q87T19pqcKBfyzqpajS7nJ/T6p71cAJ9sNNDYXGkG8FFLRVBiOCidhDLb5UDhBD1l8 DHpFZbPdRVkw2FckoUo6M5Fl6WiI82aP+x2UVrve9RNXjuqwQ5neY34HFjlcPckWht c5E5PVJlQ4zDXS77FIwjG7CfRp7hQNqNouxYfnfadk6txW/ixwp80YOPb8BtWhEqb8 cm6+uYek+h9tSGkXZEQJj1F+gytrVo63q4+hyIREduC0lZH5IyaV7mDbFjM78D6jfh DamUlZrGVBcYw== From: Timo Rothenpieler To: ffmpeg-devel@ffmpeg.org Date: Thu, 11 Aug 2022 00:51:54 +0200 Message-Id: <20220810225154.8435-1-timo@rothenpieler.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220810204712.3123-9-timo@rothenpieler.org> References: <20220810204712.3123-9-timo@rothenpieler.org> MIME-Version: 1.0 Subject: [FFmpeg-devel] [PATCH v2 09/11] avutil/half2float: use native _Float16 if available X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: FFmpeg development discussions and patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: FFmpeg development discussions and patches Cc: Timo Rothenpieler Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" X-TUID: lQ7jmNyPU7KG _Float16 support was available on arm/aarch64 for a while, and with gcc 12 was enabled on x86 as long as SSE2 is supported. If the target arch supports f16c, gcc emits fairly efficient assembly, taking advantage of it. This is the case on x86-64-v3 or higher. Same goes on arm, which has native float16 support. On x86, without f16c, it emulates it in software using sse2 instructions. This has shown to perform rather poorly: _Float16 full SSE2 emulation: frame=50074 fps=848 q=-0.0 size=N/A time=00:33:22.96 bitrate=N/A speed=33.9x _Float16 f16c accelerated (Zen2, --cpu=znver2): frame=50636 fps=1965 q=-0.0 Lsize=N/A time=00:33:45.40 bitrate=N/A speed=78.6x classic half2float full software implementation: frame=49926 fps=1605 q=-0.0 Lsize=N/A time=00:33:17.00 bitrate=N/A speed=64.2x Hence an additional check was introduced, that only enables use of _Float16 on x86 if f16c is being utilized. On aarch64, a similar uplift in performance is seen: RPi4 half2float full software implementation: frame= 6088 fps=126 q=-0.0 Lsize=N/A time=00:04:03.48 bitrate=N/A speed=5.06x RPi4 _Float16: frame= 6103 fps=158 q=-0.0 Lsize=N/A time=00:04:04.08 bitrate=N/A speed=6.32x Since arm/aarch64 always natively support 16 bit floats, it can always be considered fast there. I'm not aware of any additional platforms that currently support _Float16. And if there are, they should be considered non-fast until proven fast. --- configure | 13 +++++++++++++ libavutil/float2half.c | 2 ++ libavutil/float2half.h | 16 ++++++++++++++++ libavutil/half2float.c | 4 ++++ libavutil/half2float.h | 16 ++++++++++++++++ 5 files changed, 51 insertions(+) diff --git a/configure b/configure index 6761d0cb32..6ede9a5a8f 100755 --- a/configure +++ b/configure @@ -2143,6 +2143,8 @@ ARCH_FEATURES=" fast_64bit fast_clz fast_cmov + fast_float16 + float16 local_aligned simd_align_16 simd_align_32 @@ -5125,6 +5127,8 @@ elif enabled arm; then ;; esac + test_cflags -mfp16-format=ieee && add_cflags -mfp16-format=ieee + elif enabled avr32; then case $cpu in @@ -6229,6 +6233,15 @@ check_builtin sync_val_compare_and_swap "" "int *ptr; int oldval, newval; __sync check_builtin gmtime_r time.h "time_t *time; struct tm *tm; gmtime_r(time, tm)" check_builtin localtime_r time.h "time_t *time; struct tm *tm; localtime_r(time, tm)" +check_builtin float16 "" "_Float16 f16var" +if enabled float16; then + if enabled x86; then + test_cpp_condition stddef.h "defined(__F16C__)" && enable fast_float16 + elif enabled arm || enabled aarch64; then + enable fast_float16 + fi +fi + case "$custom_allocator" in jemalloc) # jemalloc by default does not use a prefix diff --git a/libavutil/float2half.c b/libavutil/float2half.c index dba14cef5d..7002612194 100644 --- a/libavutil/float2half.c +++ b/libavutil/float2half.c @@ -20,6 +20,7 @@ void ff_init_float2half_tables(float2half_tables *t) { +#if !HAVE_FAST_FLOAT16 for (int i = 0; i < 256; i++) { int e = i - 127; @@ -50,4 +51,5 @@ void ff_init_float2half_tables(float2half_tables *t) t->shifttable[i|0x100] = 13; } } +#endif } diff --git a/libavutil/float2half.h b/libavutil/float2half.h index b8c9cdfc4f..437666966b 100644 --- a/libavutil/float2half.h +++ b/libavutil/float2half.h @@ -20,21 +20,37 @@ #define AVUTIL_FLOAT2HALF_H #include +#include "intfloat.h" + +#include "config.h" typedef struct float2half_tables { +#if HAVE_FAST_FLOAT16 + uint8_t dummy; +#else uint16_t basetable[512]; uint8_t shifttable[512]; +#endif } float2half_tables; void ff_init_float2half_tables(float2half_tables *t); static inline uint16_t float2half(uint32_t f, const float2half_tables *t) { +#if HAVE_FAST_FLOAT16 + union { + _Float16 f; + uint16_t i; + } u; + u.f = av_int2float(f); + return u.i; +#else uint16_t h; h = t->basetable[(f >> 23) & 0x1ff] + ((f & 0x007fffff) >> t->shifttable[(f >> 23) & 0x1ff]); return h; +#endif } #endif /* AVUTIL_FLOAT2HALF_H */ diff --git a/libavutil/half2float.c b/libavutil/half2float.c index baac8e4093..ff198a8187 100644 --- a/libavutil/half2float.c +++ b/libavutil/half2float.c @@ -18,6 +18,7 @@ #include "libavutil/half2float.h" +#if !HAVE_FAST_FLOAT16 static uint32_t convertmantissa(uint32_t i) { int32_t m = i << 13; // Zero pad mantissa bits @@ -33,9 +34,11 @@ static uint32_t convertmantissa(uint32_t i) return m | e; // Return combined number } +#endif void ff_init_half2float_tables(half2float_tables *t) { +#if !HAVE_FAST_FLOAT16 t->mantissatable[0] = 0; for (int i = 1; i < 1024; i++) t->mantissatable[i] = convertmantissa(i); @@ -60,4 +63,5 @@ void ff_init_half2float_tables(half2float_tables *t) t->offsettable[31] = 2048; t->offsettable[32] = 0; t->offsettable[63] = 2048; +#endif } diff --git a/libavutil/half2float.h b/libavutil/half2float.h index cb58e44a1c..57ee8372fe 100644 --- a/libavutil/half2float.h +++ b/libavutil/half2float.h @@ -20,22 +20,38 @@ #define AVUTIL_HALF2FLOAT_H #include +#include "intfloat.h" + +#include "config.h" typedef struct half2float_tables { +#if HAVE_FAST_FLOAT16 + uint8_t dummy; +#else uint32_t mantissatable[3072]; uint32_t exponenttable[64]; uint16_t offsettable[64]; +#endif } half2float_tables; void ff_init_half2float_tables(half2float_tables *t); static inline uint32_t half2float(uint16_t h, const half2float_tables *t) { +#if HAVE_FAST_FLOAT16 + union { + _Float16 f; + uint16_t i; + } u; + u.i = h; + return av_float2int(u.f); +#else uint32_t f; f = t->mantissatable[t->offsettable[h >> 10] + (h & 0x3ff)] + t->exponenttable[h >> 10]; return f; +#endif } #endif /* AVUTIL_HALF2FLOAT_H */