From c74c3e0ba75ea10f93d8d40e4c796d1c442c070b Mon Sep 17 00:00:00 2001 From: Anton Khirnov Date: Mon, 18 Oct 2021 12:12:08 +0200 Subject: interp: add 2D Lagrangian interpolation in C --- _interp_c_template.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 59 insertions(+) create mode 100644 _interp_c_template.c (limited to '_interp_c_template.c') diff --git a/_interp_c_template.c b/_interp_c_template.c new file mode 100644 index 0000000..e1c5f8a --- /dev/null +++ b/_interp_c_template.c @@ -0,0 +1,59 @@ + +#define JOIN2(a, b) a ## _ ## b +#define FUNC2(name, stencil) JOIN2(name, stencil) +#define FUNC(name) FUNC2(name, STENCIL) + +void FUNC(interp2d)(const double *src_start, const double *src_step, + const double *src_val, + const int *src_stride, const int *src_len, + int nb_points, const double *x_vals, const double *y_vals, + double *dst) +{ + for (int pt = 0; pt < nb_points; pt++) { + const double x = x_vals[pt]; + const double y = y_vals[pt]; + + const int idx_x = (x - src_start[0]) / src_step[0] - (STENCIL / 2 - 1); + const int idx_y = (y - src_start[1]) / src_step[1] - (STENCIL / 2 - 1); + + const double src_x = idx_x * src_step[0] + src_start[0]; + const double src_y = idx_y * src_step[1] + src_start[1]; + + double fact[2][STENCIL]; + + double ret = 0.0; + + if (idx_x < 0 || idx_x > src_len[0] - STENCIL || + idx_y < 0 || idx_y > src_len[1] - STENCIL) { + ret = NAN; + goto output; + } + + for (int i = 0; i < STENCIL; i++) { + double fact_x = 1.0; + double fact_y = 1.0; + + for (int j = 0; j < STENCIL; j++) { + if (i == j) + continue; + + fact_x *= (x - (src_x + j * src_step[0])) / (src_step[0] * (i - j)); + fact_y *= (y - (src_y + j * src_step[1])) / (src_step[1] * (i - j)); + } + + fact[0][i] = fact_x; + fact[1][i] = fact_y; + } + + for (int j = 0; j < STENCIL; j++) { + double val = 0.0; + + for (int i = 0; i < STENCIL; i++) + val += fact[0][i] * src_val[(idx_y + j) * src_stride[1] + (idx_x + i) * src_stride[0]]; + + ret += fact[1][j] * val; + } +output: + dst[pt] = ret; + } +} -- cgit v1.2.3