1 files changed, 328 insertions, 0 deletions
diff --git a/ell_relax.c b/ell_relax.c
new file mode 100644
index 0000000..f51c671
--- /dev/null
+++ b/ell_relax.c
@@ -0,0 +1,328 @@
+/*
+ * Copyright 2018 Anton Khirnov <anton@khirnov.net>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <float.h>
+#include <errno.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "common.h"
+#include "ell_relax.h"
+#include "log.h"
+
+#define FD_STENCIL_MAX 1
+
+struct EllRelaxInternal {
+    ptrdiff_t stride;
+    double *u_base;
+    double *rhs_base;
+    double *residual_base;
+    double *diff_coeffs_base[ELL_RELAX_DIFF_COEFF_NB];
+};
+
+static const struct {
+    unsigned int stride_idx;
+    unsigned int is_upper;
+} boundary_def[] = {
+    [ELL_RELAX_BOUNDARY_00] = {
+        .stride_idx = 0,
+        .is_upper   = 0
+    },
+    [ELL_RELAX_BOUNDARY_01] = {
+        .stride_idx = 0,
+        .is_upper   = 1,
+    },
+    [ELL_RELAX_BOUNDARY_10] = {
+        .stride_idx = 1,
+        .is_upper   = 0,
+    },
+    [ELL_RELAX_BOUNDARY_11] = {
+        .stride_idx = 1,
+        .is_upper   = 1,
+    },
+};
+
+static inline void
+derivatives_calc(EllRelaxContext *ctx, double *dst, ptrdiff_t idx, ptrdiff_t stride)
+{
+    const double *u = ctx->u;
+    const double dx = ctx->step[0];
+    const double dy = ctx->step[1];
+
+    dst[ELL_RELAX_DIFF_COEFF_00] = u[idx];
+    dst[ELL_RELAX_DIFF_COEFF_10] = (u[idx + 1]      - u[idx - 1])      / (2.0 * dx);
+    dst[ELL_RELAX_DIFF_COEFF_01] = (u[idx + stride] - u[idx - stride]) / (2.0 * dy);
+
+    dst[ELL_RELAX_DIFF_COEFF_20] = (u[idx + 1]      - 2.0 * u[idx] + u[idx - 1])      / (SQR(dx));
+    dst[ELL_RELAX_DIFF_COEFF_02] = (u[idx + stride] - 2.0 * u[idx] + u[idx - stride]) / (SQR(dy));
+
+    dst[ELL_RELAX_DIFF_COEFF_11] = (u[idx + 1 + stride] - u[idx + stride - 1] - u[idx - stride + 1] + u[idx - stride - 1]) / (4.0 * dx * dy);
+}
+
+static void residual_calc(EllRelaxContext *ctx)
+{
+    EllRelaxInternal *priv = ctx->priv;
+
+    for (int idx1 = 0; idx1 < ctx->domain_size[1]; idx1++)
+        for (int idx0 = 0; idx0 < ctx->domain_size[0]; idx0++) {
+            ptrdiff_t idx = idx1 * priv->stride + idx0;
+
+            double u[ELL_RELAX_DIFF_COEFF_NB];
+            double res;
+
+            derivatives_calc(ctx, u, idx, priv->stride);
+
+            res = -ctx->rhs[idx];
+            for (int i = 0; i < ARRAY_ELEMS(u); i++)
+                res += u[i] * ctx->diff_coeffs[i][idx];
+
+            ctx->residual[idx] = res;
+        }
+
+    for (int i = 0; i < ARRAY_ELEMS(ctx->boundaries); i++) {
+        const ptrdiff_t strides[2] = { 1, priv->stride };
+        const int si = boundary_def[i].stride_idx;
+        const ptrdiff_t stride_boundary = strides[si];
+        const ptrdiff_t stride_offset   = strides[!si];
+        const size_t size_boundary      = ctx->domain_size[si];
+        const size_t size_offset        = ctx->domain_size[!si];
+
+        double *res = ctx->residual + boundary_def[i].is_upper * ((size_offset - 1) * stride_offset);
+
+        if (ctx->boundaries[i].type == ELL_RELAX_BC_TYPE_FIXVAL) {
+            for (size_t j = 0; j < size_boundary; j++) {
+                *res = 0.0;
+                res += stride_boundary;
+            }
+        }
+    }
+}
+
+static void boundaries_apply_fixval(double *dst, ptrdiff_t dst_stride,
+                                    const double *src,
+                                    size_t boundary_size, ptrdiff_t boundary_stride,
+                                    int is_upper)
+{
+    for (size_t i = 0; i < boundary_size; i++) {
+        *dst = *src;
+        dst += dst_stride;
+        src++;
+    }
+}
+
+static void boundaries_apply_fixdiff(double *dst, ptrdiff_t dst_stride,
+                                    const double *src,
+                                    size_t boundary_size, ptrdiff_t boundary_stride,
+                                    int is_upper)
+{
+    if (!is_upper)
+        boundary_stride *= -1;
+
+    for (size_t i = 0; i < boundary_size; i++) {
+        for (int i = 1; i <= FD_STENCIL_MAX; i++)
+            dst[boundary_stride * i] = dst[-boundary_stride * i];
+
+        dst += dst_stride;
+    }
+}
+
+static void boundaries_apply(EllRelaxContext *ctx)
+{
+    EllRelaxInternal *priv = ctx->priv;
+    const ptrdiff_t strides[2] = { 1, priv->stride };
+
+    for (int i = 0; i < ARRAY_ELEMS(ctx->boundaries); i++) {
+        const int si = boundary_def[i].stride_idx;
+        const ptrdiff_t stride_boundary = strides[si];
+        const ptrdiff_t stride_offset   = strides[!si];
+        const size_t size_boundary      = ctx->domain_size[si];
+        const size_t size_offset        = ctx->domain_size[!si];
+
+        double *dst = ctx->u + boundary_def[i].is_upper * ((size_offset - 1) * stride_offset);
+
+        switch (ctx->boundaries[i].type) {
+        case ELL_RELAX_BC_TYPE_FIXVAL:
+            boundaries_apply_fixval(dst, stride_boundary, ctx->boundaries[i].val, size_boundary,
+                                    stride_offset, boundary_def[i].is_upper);
+            break;
+        case ELL_RELAX_BC_TYPE_FIXDIFF:
+            boundaries_apply_fixdiff(dst, stride_boundary, ctx->boundaries[i].val, size_boundary,
+                                     stride_offset, boundary_def[i].is_upper);
+            break;
+        }
+    }
+}
+
+int mg2di_ell_relax_step(EllRelaxContext *ctx)
+{
+    EllRelaxInternal *priv = ctx->priv;
+    const double cfl_fac = (1.0 / 4.0) * ctx->step[0] * ctx->step[1];
+
+    for (int idx1 = 0; idx1 < ctx->domain_size[1]; idx1++)
+        for (int idx0 = 0; idx0 < ctx->domain_size[0]; idx0++) {
+            ptrdiff_t idx = idx1 * priv->stride + idx0;
+
+            ctx->u[idx] += cfl_fac * ctx->residual[idx];
+        }
+
+    boundaries_apply(ctx);
+    residual_calc(ctx);
+
+    return 0;
+}
+
+int mg2di_ell_relax_init(EllRelaxContext *ctx)
+{
+    EllRelaxInternal *priv = ctx->priv;
+    int ret;
+
+    if (ctx->fd_stencil == 0 || ctx->fd_stencil > FD_STENCIL_MAX) {
+        mg2di_log(&ctx->logger, 0, "Invalid finite difference stencil: %zd\n",
+                  ctx->fd_stencil);
+        return -EINVAL;
+    }
+
+    if (ctx->step[0] <= DBL_EPSILON || ctx->step[1] <= DBL_EPSILON) {
+        mg2di_log(&ctx->logger, 0, "Spatial step size too small\n");
+        return -EINVAL;
+    }
+
+    for (int i = 0; i < ARRAY_ELEMS(ctx->boundaries); i++) {
+        if (ctx->boundaries[i].type == ELL_RELAX_BC_TYPE_FIXDIFF) {
+           for (int k = 0; k < ctx->domain_size[boundary_def[i].stride_idx]; k++)
+               if (ctx->boundaries[i].val[k] != 0.0) {
+                   mg2di_log(&ctx->logger, 0, "Only zero boundary derivative supported\n");
+                   return -ENOSYS;
+               }
+        }
+    }
+
+    boundaries_apply(ctx);
+    residual_calc(ctx);
+
+    return 0;
+}
+
+static int ell_relax_arrays_alloc(EllRelaxContext *ctx, const size_t domain_size[2])
+{
+    EllRelaxInternal *priv = ctx->priv;
+
+    const size_t ghosts = FD_STENCIL_MAX;
+    const size_t size_padded[2] = {
+        domain_size[0] + 2 * ghosts,
+        domain_size[1] + 2 * ghosts,
+    };
+    const size_t stride = size_padded[0];
+    const size_t start_offset = ghosts * stride + ghosts;
+    const size_t arr_size = size_padded[0] * size_padded[1];
+    int ret;
+
+    ret = posix_memalign((void**)&priv->u_base, 32, sizeof(*priv->u_base) * arr_size);
+    if (ret != 0)
+        return -ret;
+    ctx->u        = priv->u_base + start_offset;
+    ctx->u_stride = stride;
+
+    ret = posix_memalign((void**)&priv->rhs_base, 32, sizeof(*priv->rhs_base) * arr_size);
+    if (ret != 0)
+        return -ret;
+    ctx->rhs        = priv->rhs_base + start_offset;
+    ctx->rhs_stride = stride;
+
+    ret = posix_memalign((void**)&priv->residual_base, 32, sizeof(*priv->residual_base) * arr_size);
+    if (ret != 0)
+        return -ret;
+    memset(priv->residual_base, 0, sizeof(*priv->residual_base) * arr_size);
+    ctx->residual        = priv->residual_base + start_offset;
+    ctx->residual_stride = stride;
+
+    for (int i = 0; i < ARRAY_ELEMS(ctx->diff_coeffs); i++) {
+        ret = posix_memalign((void**)&priv->diff_coeffs_base[i], 32,
+                             sizeof(*priv->diff_coeffs_base[i]) * arr_size);
+        if (ret != 0)
+            return -ret;
+        ctx->diff_coeffs[i] = priv->diff_coeffs_base[i] + start_offset;
+    }
+    ctx->diff_coeffs_stride = stride;
+
+    priv->stride = stride;
+
+    for (int i = 0; i < ARRAY_ELEMS(ctx->boundaries); i++) {
+        const size_t boundary_size = domain_size[boundary_def[i].stride_idx];
+        ret = posix_memalign((void**)&ctx->boundaries[i].val, 32,
+                             sizeof(*ctx->boundaries[i].val) * boundary_size);
+        if (ret != 0)
+            return -ret;
+        ctx->boundaries[i].val_len = boundary_size;
+    }
+
+    return 0;
+}
+
+EllRelaxContext *mg2di_ell_relax_alloc(size_t domain_size[2])
+{
+    EllRelaxContext *ctx;
+    EllRelaxInternal *priv;
+    int ret;
+
+    ctx = calloc(1, sizeof(*ctx));
+    if (!ctx)
+        return NULL;
+
+    ctx->priv = calloc(1, sizeof(*ctx->priv));
+    if (!ctx->priv)
+        goto fail;
+    priv = ctx->priv;
+
+    if (!domain_size[0] || !domain_size[1] ||
+        domain_size[0] > SIZE_MAX / domain_size[1])
+        goto fail;
+
+    ret = ell_relax_arrays_alloc(ctx, domain_size);
+    if (ret < 0)
+        goto fail;
+
+    ctx->domain_size[0] = domain_size[0];
+    ctx->domain_size[1] = domain_size[1];
+
+    return ctx;
+fail:
+    mg2di_ell_relax_free(&ctx);
+    return NULL;
+}
+
+void mg2di_ell_relax_free(EllRelaxContext **pctx)
+{
+    EllRelaxContext *ctx = *pctx;
+
+    if (!ctx)
+        return;
+
+    free(ctx->priv->u_base);
+    free(ctx->priv->rhs_base);
+    free(ctx->priv->residual_base);
+    for (int i = 0; i < ARRAY_ELEMS(ctx->priv->diff_coeffs_base); i++)
+        free(ctx->priv->diff_coeffs_base[i]);
+    free(ctx->priv);
+
+    for (int i = 0; i < ARRAY_ELEMS(ctx->boundaries); i++)
+        free(ctx->boundaries[i].val);
+
+    free(ctx);
+    *pctx = NULL;
+}