添加通道中的所有元素

Question

是否存在允许人们在通道中添加所有元素的内在因素？我正在使用Neon将8个数字相乘,我需要对结果求和.这里有一些释义代码来展示我目前正在做的事情(这可能会被优化):

int16_t p[8], q[8], r[8];
int32_t sum;
int16x8_t pneon, qneon, result;

p[0] = some_number;
p[1] = some_other_number; 
//etc etc
pneon = vld1q_s16(p);

q[0] = some_other_other_number;
q[1] = some_other_other_other_number;
//etc etc
qneon = vld1q_s16(q);
result = vmulq_s16(p,q);
vst1q_s16(r,result);
sum = ((int32_t) r[0] + (int32_t) r[1] + ... //etc );

有一个更好的方法吗？

Answer 1

如果您的目标是较新的arm 64位体系结构，那么ADDV就是适合您的正确说明。

这是您的代码与之搭配的样子。

qneon = vld1q_s16(q);
result = vmulq_s16(p,q);
sum = vaddvq_s16(result);

而已。只需一条指令即可汇总向量寄存器中的所有通道。

可悲的是，该指令在较旧的32位手臂体系结构中没有。

Answer 2

像这样的东西应该工作得非常理想（警告：未经测试）

const int16x4_t result_low = vget_low_s16(result); // Extract low 4 elements
const int16x4_t result_high = vget_high_s16(result); // Extract high 4 elements
const int32x4_t twopartsum = vaddl_s16(result_low, result_high); // Extend to 32 bits and add (4 partial 32-bit sums are formed)
const int32x2_t twopartsum_low = vget_low_s32(twopartsum); // Extract 2 low 32-bit partial sums
const int32x2_t twopartsum_high = vget_high_s32(twopartsum); // Extract 2 high 32-bit partial sums
const int32x2_t fourpartsum = vadd_s32(twopartsum_low, twopartsum_high); // Add partial sums (2 partial 32-bit sum are formed)
const int32x2_t eightpartsum = vpadd_s32(fourpartsum, fourpartsum); // Final reduction
const int32_t sum = vget_lane_s32(eightpartsum, 0); // Move to general-purpose registers