From 05012c2e34857f224290a69afe41b3b0cd170cde Mon Sep 17 00:00:00 2001
From: Anton Khirnov <anton@khirnov.net>
Date: Mon, 2 Dec 2019 10:57:08 +0100
Subject: Add an interpolation module.

---
 interp.py | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 interp.py

diff --git a/interp.py b/interp.py
new file mode 100644
index 0000000..c57f417
--- /dev/null
+++ b/interp.py
@@ -0,0 +1,52 @@
+import numpy as np
+
+def interp1d(src_start, src_step, src_val, dst_coords, stencil):
+    idx_src   = (dst_coords / src_step - src_start - (stencil / 2 - 1)).astype(np.int)
+    src_coord = np.linspace(src_start, src_start + src_step * (src_val.shape[0] - 1),
+                            src_val.shape[0], dtype = src_val.dtype)
+
+    fact = np.zeros((stencil, ) + idx_src.shape, dtype = src_val.dtype) + 1.0
+    for i in range(stencil):
+        for j in range(stencil):
+            if i == j:
+                continue
+
+            fact[i] *= (dst_coords - src_coord[idx_src + j]) / (src_coord[idx_src + i] - src_coord[idx_src + j])
+
+    ret = np.zeros_like(dst_coords, dtype = src_val.dtype)
+    for i in range(stencil):
+        ret += fact[i] * src_val[idx_src + i]
+
+    return ret
+
+def interp2d(src_start, src_step, src_val, dst_coords, stencil):
+    ret = np.zeros_like(dst_coords[0], dtype = src_val.dtype)
+
+    idx_src = []
+    fact    = []
+    for dim in range(len(src_start)):
+        src_coord = np.linspace(src_start[dim], src_start[dim] + src_step[dim] * (src_val.shape[dim] - 1),
+                                src_val.shape[dim], dtype = src_val.dtype)
+
+        idx = ((dst_coords[dim] - src_start[dim]) / src_step[dim] - (stencil / 2 - 1)).astype(np.int)
+        f   = np.zeros((stencil, ) + idx.shape, dtype = src_val.dtype) + 1.0
+
+
+        for i in range(stencil):
+            for j in range(stencil):
+                if i == j:
+                    continue
+
+                f[i] *= (dst_coords[dim] - src_coord[idx + j]) / (src_coord[idx + i] - src_coord[idx + j])
+
+        idx_src.append(idx)
+        fact.append(f)
+
+    for i in range(stencil):
+        val = np.zeros_like(ret)
+        for j in range(stencil):
+            val += fact[1][j] * src_val[idx_src[0] + i, idx_src[1] + j]
+
+        ret += fact[0][i] * val
+
+    return ret
-- 
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