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Performance: improve XYZ to LAB conversion by ~15% #1729

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Merged
merged 1 commit into from
Jul 20, 2020
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Performance: improve XYZ to LAB conversion by ~15% #1729

merged 1 commit into from
Jul 20, 2020

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lovell
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@lovell lovell commented Jul 19, 2020

This PR switches the XYZ to LAB clipping from fmax/fmin maths library calls to instead use the simple ternary operators of VIPS_CLIP, which the compiler is able to heavily optimise.

Before:

150,596,456  ???:vips_XYZ2Lab_line [/usr/local/lib/libvips.so.42.12.3]
 46,873,827  ???:vips_col_scRGB2XYZ [/usr/local/lib/libvips.so.42.12.3]
 25,567,542  /build/glibc-5mDdLG/glibc-2.30/math/../sysdeps/x86_64/fpu/s_fmax.S:fmax [/usr/lib/x86_64-linux-gnu/libm-2.30.so]
 25,567,542  /build/glibc-5mDdLG/glibc-2.30/math/../sysdeps/x86_64/fpu/s_fmin.S:fmin [/usr/lib/x86_64-linux-gnu/libm-2.30.so]
 24,180,156  ???:vips_scRGB2XYZ_line [/usr/local/lib/libvips.so.42.12.3]
 21,563,120  /build/glibc-5mDdLG/glibc-2.30/string/../sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S:__memcpy_avx_unaligned_erms [/usr/lib/x86_64-linux-gnu/libc-2.30.so]
 18,512,200  ???:vips_sRGB2scRGB_gen [/usr/local/lib/libvips.so.42.12.3]

After:

116,498,847  ???:vips_XYZ2Lab_line [/usr/local/lib/libvips.so.42.12.3]
 46,873,827  ???:vips_col_scRGB2XYZ [/usr/local/lib/libvips.so.42.12.3]
 24,180,156  ???:vips_scRGB2XYZ_line [/usr/local/lib/libvips.so.42.12.3]
 21,562,840  /build/glibc-5mDdLG/glibc-2.30/string/../sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S:__memcpy_avx_unaligned_erms [/usr/lib/x86_64-linux-gnu/libc-2.30.so]
 18,512,200  ???:vips_sRGB2scRGB_gen [/usr/local/lib/libvips.so.42.12.3]

@lovell lovell mentioned this pull request Jul 19, 2020
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@jcupitt jcupitt merged commit ef6ad7f into libvips:master Jul 20, 2020
@lovell lovell deleted the perf-lab-clip branch July 20, 2020 13:35
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jcupitt commented Jul 20, 2020

As I remember, VIPS_FCLIP() went in when we added support for __builtin_rint / round / fabs. They all gave a nice speedup and I suppose I just assumed min and max would as well. Interesting!

Perhaps fmin/fmax should be removed? Something to think about for 8.11.

@jcupitt jcupitt mentioned this pull request Jul 20, 2020
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lovell commented Jul 20, 2020

Yes, most of the builtins are very much worth using as you'd expect, so I too was surprised to see such a difference here.

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lovell commented Jul 21, 2020

We'll need to add isnan checking to this logic as fmin/fmax implicitly provides this. This will slow things back down by ~5% but is still faster overall. PR on the way shortly.

@jcupitt jcupitt mentioned this pull request Jul 21, 2020
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jcupitt commented Jul 21, 2020

Ooop, sorry! I just reverted this until 8.11. Sure, please make a new PR.

@lovell lovell mentioned this pull request Jul 21, 2020
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