[PATCH v2] ipa: libipa: histogram: Add transform parameter to constructor

[Paul Elder]

Add a parameter to the histogram constructor that takes a transformation
function to apply to all the bins upon construction.

This is necessary notably for the rkisp1, as the values reported from
the hardware are 20 bits where the upper 16-bits are meaningful integer
values and the lower 4 bits are fractional and meant to be discarded. As
adding a right-shift parameter is probably too specialized, a generic
function is added as a parameter instead.

Signed-off-by: Paul Elder <paul.elder at ideasonboard.com>

---
This used to be "ipa: libipa: histogram: Add rshift parameter to
constructor"

Changes in v2:
- change rshift parameter to a function parameter
---
 src/ipa/libipa/histogram.cpp | 6 ++++--
 src/ipa/libipa/histogram.h   | 6 ++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/ipa/libipa/histogram.cpp b/src/ipa/libipa/histogram.cpp
index c1aac59b..2a4095f4 100644
--- a/src/ipa/libipa/histogram.cpp
+++ b/src/ipa/libipa/histogram.cpp
@@ -40,13 +40,15 @@ namespace ipa {
 /**
  * \brief Create a cumulative histogram
  * \param[in] data A pre-sorted histogram to be passed
+ * \param[in] transform The transformation function to apply to every bin
  */
-Histogram::Histogram(Span<const uint32_t> data)
+Histogram::Histogram(Span<const uint32_t> data,
+		     std::function<uint32_t(const uint32_t)> transform)
 {
 	cumulative_.reserve(data.size());
 	cumulative_.push_back(0);
 	for (const uint32_t &value : data)
-		cumulative_.push_back(cumulative_.back() + value);
+		cumulative_.push_back(cumulative_.back() + transform(value));
 }
 
 /**
diff --git a/src/ipa/libipa/histogram.h b/src/ipa/libipa/histogram.h
index 54bb2a19..89a6b550 100644
--- a/src/ipa/libipa/histogram.h
+++ b/src/ipa/libipa/histogram.h
@@ -8,9 +8,9 @@
 #pragma once
 
 #include <assert.h>
+#include <functional>
 #include <limits.h>
 #include <stdint.h>
-
 #include <vector>
 
 #include <libcamera/base/span.h>
@@ -23,7 +23,9 @@ class Histogram
 {
 public:
 	Histogram() { cumulative_.push_back(0); }
-	Histogram(Span<const uint32_t> data);
+	Histogram(Span<const uint32_t> data,
+		  std::function<uint32_t(const uint32_t)> transform =
+		  	[](uint32_t x) { return x; });
 	size_t bins() const { return cumulative_.size() - 1; }
 	uint64_t total() const { return cumulative_[cumulative_.size() - 1]; }
 	uint64_t cumulativeFrequency(double bin) const;
-- 
2.39.2