From 2bad38d89201c5c025ae9522d4e8af13e399ca58 Mon Sep 17 00:00:00 2001
From: mohammed arib <arib@bugqore.com>
Date: Thu, 23 Jul 2026 13:50:15 +0530
Subject: [PATCH] MINOR: [c] avoid signed left-shift overflow in binary varint
 decoder

---
 lang/c/src/encoding_binary.c  | 22 +++++++++++-----------
 lang/c/tests/test_avro_data.c | 13 +++++++++++++
 2 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/lang/c/src/encoding_binary.c b/lang/c/src/encoding_binary.c
index 459d5fb3db3..31c5eb9ed97 100644
--- a/lang/c/src/encoding_binary.c
+++ b/lang/c/src/encoding_binary.c
@@ -40,7 +40,7 @@ static int read_long(avro_reader_t reader, int64_t * l)
 			return EILSEQ;
 		}
 		AVRO_READ(reader, &b, 1);
-		value |= (int64_t) (b & 0x7F) << (7 * offset);
+		value |= (uint64_t) (b & 0x7F) << (7 * offset);
 		++offset;
 	}
 	while (b & 0x80);
@@ -226,9 +226,9 @@ static int read_float(avro_reader_t reader, float *f)
 	} v;
 #if AVRO_PLATFORM_IS_BIG_ENDIAN
 	AVRO_READ(reader, buf, 4);
-	v.i = ((int32_t) buf[0] << 0)
-	    | ((int32_t) buf[1] << 8)
-	    | ((int32_t) buf[2] << 16) | ((int32_t) buf[3] << 24);
+	v.i = ((uint32_t) buf[0] << 0)
+	    | ((uint32_t) buf[1] << 8)
+	    | ((uint32_t) buf[2] << 16) | ((uint32_t) buf[3] << 24);
 #else
 	AVRO_READ(reader, (void *)&v.i, 4);
 #endif
@@ -285,13 +285,13 @@ static int read_double(avro_reader_t reader, double *d)
 
 #if AVRO_PLATFORM_IS_BIG_ENDIAN
 	AVRO_READ(reader, buf, 8);
-	v.l = ((int64_t) buf[0] << 0)
-	    | ((int64_t) buf[1] << 8)
-	    | ((int64_t) buf[2] << 16)
-	    | ((int64_t) buf[3] << 24)
-	    | ((int64_t) buf[4] << 32)
-	    | ((int64_t) buf[5] << 40)
-	    | ((int64_t) buf[6] << 48) | ((int64_t) buf[7] << 56);
+	v.l = ((uint64_t) buf[0] << 0)
+	    | ((uint64_t) buf[1] << 8)
+	    | ((uint64_t) buf[2] << 16)
+	    | ((uint64_t) buf[3] << 24)
+	    | ((uint64_t) buf[4] << 32)
+	    | ((uint64_t) buf[5] << 40)
+	    | ((uint64_t) buf[6] << 48) | ((uint64_t) buf[7] << 56);
 #else
 	AVRO_READ(reader, (void *)&v.l, 8);
 #endif
diff --git a/lang/c/tests/test_avro_data.c b/lang/c/tests/test_avro_data.c
index 3a26c67e242..a194f13426b 100644
--- a/lang/c/tests/test_avro_data.c
+++ b/lang/c/tests/test_avro_data.c
@@ -272,6 +272,19 @@ static int test_int64(void)
 		avro_datum_decref(double_datum);
 	}
 
+	/* Boundary values that encode to a full-width 10-byte varint and set
+	 * the high bit on the final byte, exercising the widest shift in the
+	 * varint decoder. */
+	static const int64_t edge_values[] = {
+		INT64_MAX, INT64_MIN, INT64_MAX - 1, INT64_MIN + 1,
+		(int64_t) 1 << 62, -((int64_t) 1 << 62)
+	};
+	for (i = 0; i < (int) (sizeof(edge_values) / sizeof(edge_values[0])); i++) {
+		avro_datum_t edge_datum = avro_int64(edge_values[i]);
+		write_read_check(writer_schema, edge_datum, NULL, NULL, "long");
+		avro_datum_decref(edge_datum);
+	}
+
 	avro_datum_t  datum = avro_int64(10000);
 	test_json(datum, "10000");
 	avro_datum_decref(datum);