1 files changed, 52 insertions, 0 deletions
diff --git a/src/include/utils/ascii.h b/src/include/utils/ascii.h
index aed8019..4e3a1d4 100644
--- a/src/include/utils/ascii.h
+++ b/src/include/utils/ascii.h
@@ -13,4 +13,56 @@
 
 extern void ascii_safe_strlcpy(char *dest, const char *src, size_t destsiz);
 
+/*
+ * Verify a chunk of bytes for valid ASCII.
+ *
+ * Returns false if the input contains any zero bytes or bytes with the
+ * high-bit set. Input len must be a multiple of 8.
+ */
+static inline bool
+is_valid_ascii(const unsigned char *s, int len)
+{
+	uint64		chunk,
+				highbit_cum = UINT64CONST(0),
+				zero_cum = UINT64CONST(0x8080808080808080);
+
+	Assert(len % sizeof(chunk) == 0);
+
+	while (len > 0)
+	{
+		memcpy(&chunk, s, sizeof(chunk));
+
+		/*
+		 * Capture any zero bytes in this chunk.
+		 *
+		 * First, add 0x7f to each byte. This sets the high bit in each byte,
+		 * unless it was a zero. If any resulting high bits are zero, the
+		 * corresponding high bits in the zero accumulator will be cleared.
+		 *
+		 * If none of the bytes in the chunk had the high bit set, the max
+		 * value each byte can have after the addition is 0x7f + 0x7f = 0xfe,
+		 * and we don't need to worry about carrying over to the next byte. If
+		 * any input bytes did have the high bit set, it doesn't matter
+		 * because we check for those separately.
+		 */
+		zero_cum &= (chunk + UINT64CONST(0x7f7f7f7f7f7f7f7f));
+
+		/* Capture any set bits in this chunk. */
+		highbit_cum |= chunk;
+
+		s += sizeof(chunk);
+		len -= sizeof(chunk);
+	}
+
+	/* Check if any high bits in the high bit accumulator got set. */
+	if (highbit_cum & UINT64CONST(0x8080808080808080))
+		return false;
+
+	/* Check if any high bits in the zero accumulator got cleared. */
+	if (zero_cum != UINT64CONST(0x8080808080808080))
+		return false;
+
+	return true;
+}
+
 #endif							/* _ASCII_H_ */