py/qstr: Add support for MICROPY_QSTR_BYTES_IN_HASH=0.

This disables using qstr hashes altogether, which saves RAM and flash
(two bytes per interned string on a typical build) as well as code size.
On PYBV11 this is worth over 3k flash.

qstr comparison will now be done just by length then data. This affects
qstr_find_strn although this has a negligible performance impact as, for a
given comparison, the length and first character will ~usually be
different anyway.

String hashing (e.g. builtin `hash()` and map.c) now need to compute the
hash dynamically, and for the map case this does come at a performance
cost.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/py/qstr.h b/py/qstr.h
index 0c4fc4632..58ce285fd 100644
--- a/py/qstr.h
+++ b/py/qstr.h
@@ -60,7 +60,9 @@ enum {
 typedef size_t qstr;
 typedef uint16_t qstr_short_t;
 
-#if MICROPY_QSTR_BYTES_IN_HASH == 1
+#if MICROPY_QSTR_BYTES_IN_HASH == 0
+// No qstr_hash_t type needed.
+#elif MICROPY_QSTR_BYTES_IN_HASH == 1
 typedef uint8_t qstr_hash_t;
 #elif MICROPY_QSTR_BYTES_IN_HASH == 2
 typedef uint16_t qstr_hash_t;
@@ -82,7 +84,9 @@ typedef struct _qstr_pool_t {
     size_t is_sorted : 1;
     size_t alloc;
     size_t len;
+    #if MICROPY_QSTR_BYTES_IN_HASH
     qstr_hash_t *hashes;
+    #endif
     qstr_len_t *lengths;
     const char *qstrs[];
 } qstr_pool_t;
@@ -92,6 +96,7 @@ typedef struct _qstr_pool_t {
 void qstr_init(void);
 
 size_t qstr_compute_hash(const byte *data, size_t len);
+
 qstr qstr_find_strn(const char *str, size_t str_len); // returns MP_QSTRnull if not found
 
 qstr qstr_from_str(const char *str);