resample: port resample_neon.h to aarch64

[fbarchard]

port optimized inner_product_single and WORD2INT(x) for fixed
and floating point from 32 bit armv7 NEON to aarch64 NEON.

[tmatth]

I'm getting an assembler error with gcc 4.9 here:
Error: operand 2 should be an integer register -- fmov s0,v1
Why not:

asm ("fcvtas s0, %s[a]\n"
     "sqxtn h0, s0\n"
     "sxtl v0.4s, v0.4h\n"
     "fmov %w[ret], s0\n"
     : [ret] "=r" (ret)
     : [a] "w" (a)
     : "v0");

[fbarchard]

On Mon, Aug 8, 2016 at 8:26 PM, Tristan Matthews notifications@github.com
wrote:

In libspeexdsp/resample_neon.h
#8 (comment):

+#elif defined(FLOATING_POINT)
+#if defined(aarch64)
+static inline int32_t saturate_float_to_16bit(float a) {

• int32_t ret;
• asm ("fmov s0, %w[a]\n"

I'm getting an assembler error with gcc 4.9 here:
Error: operand 2 should be an integer register -- fmov s0,v1

doh! My bad. I've reproduced the error with gcc 4.9. It was supposed to
be:

asm ("fmov s0, *%s[a]\*n"

..

Why not:

asm ("fcvtas s0, %s[a]\n" "sqxtn h0, s0\n" "sxtl v0.4s, v0.4h\n" "fmov %w[ret], s0\n" : [ret] "=r" (ret) : [a] "w" (a) : "v0");

at the time I had trouble with clang... it said it couldnt allocate a
register. perhaps because the float is in s0, and I used s0. Reguardless,
I'm able to build your code with clang 3.8 so should be fine.
Changing it to use v1 saves a mov

     asm ("fcvtas s1, %s[a]\n"
     "sqxtn h1, s1\n"
     "sxtl v1.4s, v1.4h\n"
     "fmov %w[ret], s1\n"
     : [ret] "=r" (ret)
     : [a] "w" (a)
     : "v1");

0: 5e21c801 fcvtas s1, s0
4: 5e614821 sqxtn h1, s1
8: 0f10a421 sxtl v1.4s, v1.4h
c: 1e260020 fmov w0, s1
10: d65f03c0 ret

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[lu-zero]

Probably @sasshka might help on that.

[tmatth]

@lu-zero besides this, the existing NEON could also use some magic from @sasshka

[fbarchard]

The 64 bit NEON in this pull request, is a direct port of the 32 bit version.
Both float and short resamplers are implemented and performance is identical to arm32.
The short version is faster due to small stores and the mla pipelines nicely to 1 register.
The thumb2 32 bit version runs faster on current cpus due to smaller instructions than arm32 and aarch64.

I tested it with clang, but if you're still seeing saturate_float_to_16bit build errors (compiler bug), try a simple '=r' for the output, which will generate 2 mov's. Or use tristans suggestion, which failed on older clang versions, but the bug is fixed on current versions of clang.

[tmatth]

@fbarchard are you able to reproduce this issue by any chance?
#13

[tmatth]

@fbarchard I squashed your patch and subsequent fix for GCC into this branch:
https://git.xiph.org/?p=speexdsp.git;a=shortlog;h=refs/heads/resample-aarch64
Let me know if you're able to test.

[lu-zero]

I tested on the odroid and opened #17 to make the experience a little nicer.

[tmatth]

Merged as 8ce055a (finally!), thanks