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feat:support any num_heads for get_alibi_slope #200

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merged 1 commit into from
Apr 11, 2024
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feat:support any num_heads for get_alibi_slope #200

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5 changes: 3 additions & 2 deletions include/flashinfer/pos_enc.cuh
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Original file line number Diff line number Diff line change
Expand Up @@ -56,8 +56,9 @@ inline std::string PosEncodingModeToString(const PosEncodingMode& pos_encoding_m
}

__device__ __forceinline__ float get_alibi_slope(uint32_t head_idx, uint32_t num_heads) {
// NOTE(Zihao): here we assume that num_heads is a power of 2
return math::ptx_exp2(-8. * float(head_idx + 1) / float(num_heads));
int n = math::ptx_exp2((int)math::ptx_log2(num_heads));
return head_idx < n ? math::ptx_exp2(-8. * float(head_idx + 1) / float(n))
: math::ptx_exp2(-4. * float((head_idx + 1 - n) * 2 - 1) / float(n));
}

/*!
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