arm neon 数据类型介绍

arm neon 数据类型，定义在arm_neon.h 

/prebuilts/gcc/linux-x86/arm/arm-eabi-4.8/lib/gcc/arm-eabi/4.8/nclude/arm_neon.h 

typedef __builtin_neon_qi int8x8_t	__attribute__ ((__vector_size__ (8)));
typedef __builtin_neon_hi int16x4_t	__attribute__ ((__vector_size__ (8)));
typedef __builtin_neon_si int32x2_t	__attribute__ ((__vector_size__ (8)));
typedef __builtin_neon_di int64x1_t;
typedef __builtin_neon_sf float32x2_t	__attribute__ ((__vector_size__ (8)));
typedef __builtin_neon_poly8 poly8x8_t	__attribute__ ((__vector_size__ (8)));
typedef __builtin_neon_poly16 poly16x4_t	__attribute__ ((__vector_size__ (8)));
typedef __builtin_neon_uqi uint8x8_t	__attribute__ ((__vector_size__ (8)));
typedef __builtin_neon_uhi uint16x4_t	__attribute__ ((__vector_size__ (8)));
typedef __builtin_neon_usi uint32x2_t	__attribute__ ((__vector_size__ (8)));
typedef __builtin_neon_udi uint64x1_t;
typedef __builtin_neon_qi int8x16_t	__attribute__ ((__vector_size__ (16)));
typedef __builtin_neon_hi int16x8_t	__attribute__ ((__vector_size__ (16)));
typedef __builtin_neon_si int32x4_t	__attribute__ ((__vector_size__ (16)));
typedef __builtin_neon_di int64x2_t	__attribute__ ((__vector_size__ (16)));
typedef __builtin_neon_sf float32x4_t	__attribute__ ((__vector_size__ (16)));
typedef __builtin_neon_poly8 poly8x16_t	__attribute__ ((__vector_size__ (16)));
typedef __builtin_neon_poly16 poly16x8_t	__attribute__ ((__vector_size__ (16)));
typedef __builtin_neon_uqi uint8x16_t	__attribute__ ((__vector_size__ (16)));
typedef __builtin_neon_uhi uint16x8_t	__attribute__ ((__vector_size__ (16)));
typedef __builtin_neon_usi uint32x4_t	__attribute__ ((__vector_size__ (16)));
typedef __builtin_neon_udi uint64x2_t	__attribute__ ((__vector_size__ (16)));

数据类型格式：<类型><大小>x<向量线条数>x<数组长度>_t

例如 

uint8x16_t   无符号的int8（8个bit，相当于一个字节）,16向量线条数16，所以总的大小是 8 x 16 =128 bit，也就是16字节

uint8x16x2_t 无符号的int8（8个bit，相当于一个字节）,16向量线条数16，数组长度2，所以总的大小是 8 x 16 x 2 =256bit，也就是32字节

typedef struct uint8x16x2_t
{
  uint8x16_t val[2];
} uint8x16x2_t;