如何使用Neon SIMD将unsigned char转换为有符号整数

Question

如何使用Neon将数据类型uint8_t的变量转换为int32_t？我找不到这样做的任何内在。

Answer 1

假设您要将16 x 8位整数的向量转换为4 x 32位整数的四个向量，您可以先将解包为16位再重新打包为32位来实现此目的：

// load 8 bit vector
uint8x16_t v = vld1q_u8(p);   // load vector of 16 x 8 bits ints from p

// unpack to 16 bits
int16x8_t vl =  vreinterpretq_s16_u16(vmovl_u8(vget_low_u8(v)));   // 0..7
int16x8_t vh =  vreinterpretq_s16_u16(vmovl_u8(vget_high_u8(v)));  // 8..15

// unpack to 32 bits
int32x4_t vll = vmovl_s16(vget_low_s16(vl));           // 0..3
int32x4_t vlh = vmovl_s16(vget_high_s16(vl));          // 4..7
int32x4_t vhl = vmovl_s16(vget_low_s16(vh));           // 8..11
int32x4_t vhh = vmovl_s16(vget_high_s16(vh));          // 12..15