From 02440f670df71d26b39e924ade41e85e860deb38 Mon Sep 17 00:00:00 2001
From: Bhaskar <39916271+bhaskar0210s@users.noreply.github.com>
Date: Tue, 14 Oct 2025 17:21:11 +0530
Subject: [PATCH] fix: return inf instead of crashing when evaluate_bpb has
 zero total_bytes

Edge case: all tokens are special tokens or ignored

Return infinity to indicate no meaningful bytes were processed
---
 nanochat/loss_eval.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/nanochat/loss_eval.py b/nanochat/loss_eval.py
index d103ef6..b59b4a3 100644
--- a/nanochat/loss_eval.py
+++ b/nanochat/loss_eval.py
@@ -59,5 +59,7 @@ def evaluate_bpb(model, batches, steps, token_bytes):
     # move both to cpu, calculate bpb and return
     total_nats = total_nats.item()
     total_bytes = total_bytes.item()
+    if total_bytes == 0:
+        return float('inf')
     bpb = total_nats / (math.log(2) * total_bytes)
     return bpb