From 5b0d3f6d5ad46596e0f30c967c00e2dc2b93d8da Mon Sep 17 00:00:00 2001
From: Ed Addario <eaddario@hotmail.com>
Date: Sat, 11 Oct 2025 10:04:48 +0100
Subject: [PATCH] Automatically determine if bias error is significant

---
 src/llama-quant.cpp | 52 +++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 48 insertions(+), 4 deletions(-)

diff --git a/src/llama-quant.cpp b/src/llama-quant.cpp
index 4ad5124d1a..07a88f0fd6 100644
--- a/src/llama-quant.cpp
+++ b/src/llama-quant.cpp
@@ -637,6 +637,8 @@ static std::unordered_map<std::string, ggml_type> target_bpw_type(
         float bpw;
         size_t bytes;
         double error;
+        double mse = 0.0;
+        double proj = 0.0;
     };
 
     struct tensor_info {
@@ -1340,9 +1342,11 @@ static std::unordered_map<std::string, ggml_type> target_bpw_type(
                     const ggml_type tensor_types = compatible_candidates[i];
                     const auto bpw = (float)tensor_bpw(tensor, tensor_types);
                     const size_t bytes = tensor_bytes(tensor, tensor_types);
+                    double mse = 0.0;
+                    double proj = 0.0;
                     const auto err = estimate_error(tensor, tensor_types, f32_sample, rows_sample, values, activations,
-                        tl_quantized_buffer, tl_dequantized_buffer, tensor_lambda, slice_lambda);
-                    eval_candidates[i] = candidate_types{ tensor_types, bpw, bytes, err };
+                        tl_quantized_buffer, tl_dequantized_buffer, tensor_lambda, slice_lambda, &mse, &proj);
+                    eval_candidates[i] = candidate_types{ tensor_types, bpw, bytes, err, mse, proj };
                 }
             });
         }
@@ -1354,8 +1358,48 @@ static std::unordered_map<std::string, ggml_type> target_bpw_type(
             check_signal_handler(all);
         }
 
-        for (auto &c : eval_candidates) {
-            if (c.bytes > 0) { info.candidate.push_back(c); }
+        // Check if biasing is needed
+        bool bias_needed = false;
+        if (!lambdas.empty()) {
+            int min_mse  = -1;
+            int min_bias = -1;
+            {
+                double best_mse = std::numeric_limits<double>::infinity();
+                double best_err = std::numeric_limits<double>::infinity();
+                for (int i = 0; i < (int)eval_candidates.size(); ++i) {
+                    const auto & c = eval_candidates[i];
+                    if (c.bytes == 0) { continue; }
+                    if (c.mse  < best_mse) {
+                        best_mse = c.mse;
+                        min_mse  = i;
+                    }
+                    if (c.error < best_err) {
+                        best_err = c.error;
+                        min_bias = i;
+                    }
+                }
+            }
+
+            if (min_mse != min_bias) {
+                bias_needed = true;
+            } else {
+                double max_rel_bias = 0.0;
+                for (const auto & c : eval_candidates) {
+                    if (c.bytes == 0) { continue; }
+                    const double mse = std::max(c.mse, epsilon);
+                    const double bias_term = std::max(0.0, c.error - c.mse);
+                    const double rel = bias_term / mse;
+                    max_rel_bias = std::max(rel, max_rel_bias);
+                }
+
+                bias_needed = max_rel_bias >= 0.5; // >= 50% of MSE?
+            }
+        }
+
+        for (auto & c : eval_candidates) {
+            if (c.bytes == 0) { continue; }
+            const double final_err = bias_needed ? c.error : c.mse;
+            info.candidate.push_back(candidate_types{ c.type, c.bpw, c.bytes, final_err, c.mse, c.proj });
         }
 
         if (info.candidate.empty()) {