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# -*- coding: utf-8 -*-
# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
import triton
import triton.language as tl
from fla.ops.utils.op import exp, log
@triton.autotune(
configs=[
triton.Config({'BT': BT}, num_warps=num_warps)
for BT in [16, 32, 64]
for num_warps in [2, 4, 8]
],
key=['S']
)
@triton.jit(do_not_specialize=['T'])
def logcumsumexp_fwd_kernel(
s,
z,
T,
S: tl.constexpr,
BT: tl.constexpr
):
i_bh = tl.program_id(0)
o_i = tl.arange(0, BT)
m_s = tl.where(o_i[:, None] >= o_i[None, :], 1., 0.)
b_mp = tl.full([S,], float('-inf'), dtype=tl.float32)
b_zp = tl.zeros([S,], dtype=tl.float32)
for i_t in range(tl.cdiv(T, BT)):
p_s = tl.make_block_ptr(s + i_bh * T*S, (T, S), (S, 1), (i_t * BT, 0), (BT, S), (1, 0))
p_z = tl.make_block_ptr(z + i_bh * T*S, (T, S), (S, 1), (i_t * BT, 0), (BT, S), (1, 0))
# [BT, S]
b_s = tl.load(p_s, boundary_check=(0, 1)).to(tl.float32)
# [S,]
b_mc = tl.max(b_s, 0)
b_mc = tl.maximum(b_mp, b_mc)
b_zp = b_zp * exp(b_mp - b_mc)
# [BT, S]
b_s = exp(b_s - b_mc)
b_z = tl.dot(m_s, b_s, allow_tf32=False) + b_zp
# [S,]
b_zc = tl.max(b_z, 0)
b_mp = b_mc
b_zp = b_zc
# [BT, BS]
# small eps to prevent underflows
b_z = log(tl.where(b_z != 0, b_z, 1e-20)) + b_mc
tl.store(p_z, b_z.to(p_z.dtype.element_ty), boundary_check=(0, 1))
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