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struct Matrix { | |
float *base; // pointer to first element | |
int m; // number of rows | |
int n; // number of columns | |
int drow; // row stride | |
Matrix(float *base, int m, int n, int drow = 0) : base(base), m(m), n(n), drow(drow ? drow : n) { } | |
INLINE float& operator()(int i, int j) { | |
// assert(0 <= i && i < m); | |
// assert(0 <= j && j < n); | |
return base[i*drow + j]; | |
} | |
// block starting at i, j with clamped size mb, nb | |
Matrix block(int i, int j, int mb, int nb) { | |
return {base + i*drow + j, clamp(mb, 0, m - i), clamp(nb, 0, n - j), drow}; | |
} | |
}; | |
void gemm_ijk(Matrix C, Matrix A, Matrix B) { | |
int m = C.m; | |
int n = C.n; | |
int p = A.n; | |
assert(A.m == m); | |
assert(B.n == n); | |
assert(B.m == p); | |
for (int i = 0; i < m; i++) { | |
for (int j = 0; j < n; j++) { | |
for (int k = 0; k < p; k++) { | |
// MSVC 2017 generates 3 IMULs + ADDs per inner loop. That's 3 billion IMULs + 3 billion ADDs for 1000x1000. | |
// ICC recognizes and reduces the induction variables, so there's only two ADDs per inner loop. | |
C(i, j) += A(i, k) * B(k, j); | |
} | |
} | |
} | |
} | |
// For 1000x1000, this is 2x faster than gemm_ijk on MSVC and the same speed as gemm_ijk on ICC. | |
void gemm_ijk_ptr(Matrix C, Matrix A, Matrix B) { | |
int m = C.m; | |
int n = C.n; | |
int p = A.n; | |
assert(A.m == m); | |
assert(B.n == n); | |
assert(B.m == p); | |
for (int i = 0; i < m; i++) { | |
for (int j = 0; j < n; j++) { | |
float *Cptr = &C(i, j); | |
float *Aptr = &A(i, 0); | |
float *Bptr = &B(0, j); | |
for (int k = 0; k < p; k++) { | |
// C(i, j) += A(i, k) * B(k, j); | |
*Cptr += *Aptr * *Bptr; | |
Aptr++; | |
Bptr += B.drow; | |
} | |
} | |
} | |
} | |
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