From 898db41afa6c84c96a09f3075d072fc2e498477e Mon Sep 17 00:00:00 2001
From: Vitaliy Gulevskiy <vvgulevskiy@users.noreply.github.com>
Date: Sun, 28 Jun 2026 23:01:07 +0300
Subject: [PATCH] Add fht2rdbu and fht2rubd resampling methods

---
 adrtlib/demo.py             |   3 +
 adrtlib/ref/fht2resample.py | 120 ++++++++++++++++++++++++++++++++++++
 2 files changed, 123 insertions(+)
 create mode 100644 adrtlib/ref/fht2resample.py

diff --git a/adrtlib/demo.py b/adrtlib/demo.py
index df7402b..d3d5d57 100755
--- a/adrtlib/demo.py
+++ b/adrtlib/demo.py
@@ -12,6 +12,7 @@
 from adrtlib.ref.fht2ms import fht2ms
 from adrtlib.ref.fht2mt import fht2mt
 from adrtlib.ref.fht2sp import fht2sp
+from adrtlib.ref.fht2resample import fht2rdbu, fht2rubd
 from adrtlib.ref.khanipov import khanipov as khanipov_np
 from adrtlib.ref.fht2ids import (
     fht2ids as fht2ids_orig,
@@ -155,6 +156,8 @@ def get_adrt_func_by_name(func_name: str) -> Func:
     fht2ms,
     fht2mt,
     fht2sp,
+    fht2rdbu,
+    fht2rubd,
     asd2,
     khanipov,
 ]
diff --git a/adrtlib/ref/fht2resample.py b/adrtlib/ref/fht2resample.py
new file mode 100644
index 0000000..94aab4d
--- /dev/null
+++ b/adrtlib/ref/fht2resample.py
@@ -0,0 +1,120 @@
+from __future__ import annotations
+
+import math
+from collections.abc import Callable
+
+from adrtlib.ref.common import ADRTResult, Image, OpCount, round05, Sign
+from adrtlib.ref.fht2d import fht2dt
+
+
+def bit_floor(n: int) -> int:
+    """Largest power of two not greater than n (cf. C++ std::bit_floor)."""
+    if n <= 0:
+        return 1
+    if n & (n - 1) == 0:
+        return n
+    return 1 << (n.bit_length() - 1)
+
+
+def bit_ceil(n: int) -> int:
+    """Smallest power of two not less than n (cf. C++ std::bit_ceil)."""
+    if n <= 1:
+        return 1
+    return 1 << (n - 1).bit_length()
+
+
+def calculate_new_dimensions(
+    h: int,
+    w: int,
+    height_round: Callable[[int], int],
+) -> tuple[int, int]:
+    h_new = height_round(h)
+    w_new = round05(w * h_new / h)
+    return h_new, w_new
+
+
+def resize_with_integral_brightness(
+    image: list[list[float]],
+    new_h: int,
+    new_w: int,
+    scale_weighted_sum: bool = False,
+) -> ADRTResult:
+    h = len(image)
+    w = len(image[0]) if h > 0 else 0
+
+    if new_h == h and new_w == w:
+        return ADRTResult(image, OpCount(0))
+
+    new_image = [[0.0 for _ in range(new_w)] for _ in range(new_h)]
+
+    if h == 0 or w == 0:
+        return ADRTResult(new_image, OpCount(0))
+
+    h_ratio = h / new_h
+    w_ratio = w / new_w
+    scale_factor = (h * w) / (new_h * new_w)
+
+    if scale_weighted_sum:
+        sample_scale = scale_factor / (h_ratio * h_ratio * w_ratio)
+    else:
+        sample_scale = scale_factor / (h_ratio * h_ratio * w_ratio * w_ratio)
+
+    op_count = 0
+
+    for y in range(new_h):
+        h_start = y * h_ratio
+        h_end = (y + 1) * h_ratio
+
+        for x in range(new_w):
+            w_start = x * w_ratio
+            w_end = (x + 1) * w_ratio
+
+            acc = 0.0
+
+            y_min = max(0, math.floor(h_start))
+            y_max = min(h, math.ceil(h_end))
+            x_min = max(0, math.floor(w_start))
+            x_max = min(w, math.ceil(w_end))
+
+            for y0 in range(y_min, y_max):
+                for x0 in range(x_min, x_max):
+                    h_overlap = min(y0 + 1, h_end) - max(y0, h_start)
+                    w_overlap = min(x0 + 1, w_end) - max(x0, w_start)
+                    overlap_area = h_overlap * w_overlap
+                    product = image[y0][x0] * overlap_area * sample_scale
+                    acc += product
+
+            op_count += (y_max - y_min) * (x_max - x_min) * 2 - 1
+
+            new_image[y][x] = acc
+
+    return ADRTResult(new_image, OpCount(op_count))
+
+
+def _fht2resample(
+    img: Image,
+    sign: Sign,
+    height_round: Callable[[int], int],
+) -> ADRTResult:
+    h = len(img)
+    w = len(img[0]) if h > 0 else 0
+    h_new, w_new = calculate_new_dimensions(h, w, height_round)
+
+    pre_res = resize_with_integral_brightness(img, h_new, w_new, True)
+    fht_res = fht2dt(pre_res.image, sign)
+    post_res = resize_with_integral_brightness(fht_res.image, h, w, False)
+
+    return ADRTResult(
+        post_res.image,
+        OpCount(pre_res.op_count + fht_res.op_count + post_res.op_count),
+    )
+
+
+def fht2rdbu(img: Image, sign: Sign = -1) -> ADRTResult:
+    """Resample Down — Brady-Yong — Up."""
+    return _fht2resample(img, sign, bit_floor)
+
+
+def fht2rubd(img: Image, sign: Sign = -1) -> ADRTResult:
+    """Resample Up — Brady-Yong — Down."""
+    return _fht2resample(img, sign, bit_ceil)