NN: apply q7 fix from upstream.
* Title: arm_softmax_q7.c
* Description: Q7 softmax function
*
- * $Date: 17. January 2018
+ * $Date: 20. February 2018
* $Revision: V.1.0.0
*
* Target Processor: Cortex-M cores
@@ -64,43 +64,56 @@ void arm_softmax_q7(const q7_t * vec_in, const uint16_t dim_vec, q7_t * p_out)
{
q31_t sum;
int16_t i;
- q15_t min, max;
- max = -257;
- min = 257;
+ uint8_t shift;
+ q15_t base;
+ base = -257;
+
+ /* We first search for the maximum */
for (i = 0; i < dim_vec; i++)
{
- if (vec_in[i] > max)
- {
- max = vec_in[i];
- }
- if (vec_in[i] < min)
+ if (vec_in[i] > base)
{
- min = vec_in[i];
+ base = vec_in[i];
}
}
- /* we ignore really small values
- * anyway, they will be 0 after shrinking
- * to q7_t
+ /*
+ * So the base is set to max-8, meaning
+ * that we ignore really small values.
+ * anyway, they will be 0 after shrinking to q7_t.
*/
- if (max - min > 8)
- {
- min = max - 8;
- }
+ base = base - 8;
sum = 0;
for (i = 0; i < dim_vec; i++)
{
- sum += 0x1 << (vec_in[i] - min);
+ if (vec_in[i] > base)
+ {
+ shift = (uint8_t)__USAT(vec_in[i] - base, 5);
+ sum += 0x1 << shift;
}
+ }
+
+ /* This is effectively (0x1 << 20) / sum */
+ int output_base = 0x100000 / sum;
+ /*
+ * Final confidence will be output_base >> ( 13 - (vec_in[i] - base) )
+ * so 128 (0x1<<7) -> 100% confidence when sum = 0x1 << 8, output_base = 0x1 << 12
+ * and vec_in[i]-base = 8
+ */
for (i = 0; i < dim_vec; i++)
{
- /* we leave 7-bit dynamic range, so that 128 -> 100% confidence */
- p_out[i] = (q7_t) __SSAT(((0x1 << (vec_in[i] - min + 20)) / sum) >> 13, 8);
+ if (vec_in[i] > base)
+ {
+ /* Here minimum value of 13+base-vec_in[i] will be 5 */
+ shift = (uint8_t)__USAT(13+base-vec_in[i], 5);
+ p_out[i] = (q7_t) __SSAT((output_base >> shift), 8);
+ } else {
+ p_out[i] = 0;
+ }
}
-
}
/**
