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activation: use dedicated fixed-point λ for SeLU (fixes #1287) #1296

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activation: use dedicated fixed-point λ for SeLU (fixes #1287) #1296

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624e00a
activation: use dedicated fixed-point λ for SeLU (fixes #1287)
valerioedu May 11, 2025
82e3ddc
2 integer bits correction
valerioedu May 11, 2025
9536f29
ufixed and trailing whitespace fix I hope
valerioedu May 12, 2025
ed6eaeb
maybe trailing whitespace could be caused by single line notation?
valerioedu May 12, 2025
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24 changes: 16 additions & 8 deletions hls4ml/templates/vivado/nnet_utils/nnet_activation.h
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Original file line number Diff line number Diff line change
Expand Up @@ -717,19 +717,27 @@ template <class data_T, class res_T, typename CONFIG_T> void selu(data_T data[CO
initialized = true;
}

#pragma HLS PIPELINE
typedef ap_ufixed<16,2> selu_const_t;
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Would just 1 integer bit be enough?

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@valerioedu valerioedu May 12, 2025 •
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yeah, kept one more just to be sure, do you want me to bring it to 1?

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I think 1 makes sense, since the number is in the range.

static const selu_const_t lambda = 1.0507009873554805;

data_T datareg;
// Index into the lookup table based on data
int index;
#pragma HLS PIPELINE
for (int ii = 0; ii < CONFIG_T::n_in; ii++) {
datareg = data[ii];
data_T datareg = data[ii];

if (datareg >= 0) {
res[ii] = res_T(1.0507009873554804934193349852946) * datareg;
// Positive branch y = λ · x
res[ii] = lambda * datareg;
} else {
index = datareg * CONFIG_T::table_size / -8;
if (index > CONFIG_T::table_size - 1)
// Negative branch y = table(x)
int index = datareg * CONFIG_T::table_size / -8;

// clamp index to [0, table_size-1]
if (index < 0)
index = 0;
else if (index > CONFIG_T::table_size - 1) {
index = CONFIG_T::table_size - 1;
}

res[ii] = selu_table[index];
}
}
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