如何使用霓虹燈SIMD將無符號字符轉換爲有符號整數

Question

如何使用霓虹燈將數據類型爲uint8_t的變量轉換爲int32_t？我找不到任何內在的做法。

Answer 1

假設要的16×8位整數的向量轉換爲4×32位整數四個矢量，則可以通過首先打開包裝到16位做到這一點，然後再次以32位：

// 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