Port SIMD code to ARM NEON #90

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1. aqrit commented on Oct 22, 2021

   

   aqrit

   on Oct 22, 2021

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   Possible approach for parsing of 8 UTF-16 digits (assumes little endian).
   Note: I know very little about ARM or NEON.

   uint16x8_t x = vld1q_u16(src);
   x = vsubq_u16(x, vdupq_n_u16(0x0030));
   uint8x8_t m = vqmovn_u16(vcgtq_u16(x, vdupq_n_u16(0x0009)));
   if(vget_lane_u64(vreinterpret_u64_u8(m), 0) == 0) {	// all 8 chars are digits
   	static const uint32_t mul1[4] = {
   		0x03E80064, 0x0000A0001, // 100 + (1000 << 16), 1 + (10 << 16)
   		0x03E80064, 0x0000A0001
   	};
   	uint32x4_t v = vmulq_u32(vreinterpretq_u32_u16(x), vld1q_u32(mul1));
   	uint32x2_t t = vpaddl_u16(vshrn_n_u32(v, 16));
   	uint32_t a = vget_lane_u32(t, 0);
   	uint32_t b = vget_lane_u32(t, 1);
   	return (a * 10000) + b;
   }