paleolimbot commented on code in PR #276:
URL: https://github.com/apache/arrow-nanoarrow/pull/276#discussion_r1296598699
##########
src/nanoarrow/buffer_inline.h:
##########
@@ -236,6 +248,46 @@ static inline int8_t ArrowBitGet(const uint8_t* bits,
int64_t i) {
return (bits[i >> 3] >> (i & 0x07)) & 1;
}
+static inline void ArrowBitmapUnpackInt8Unsafe(const uint8_t* bits, int64_t
start_offset,
+ int64_t length, int8_t* out) {
+ if (length == 0) {
+ return;
+ }
+
+ const int64_t i_begin = start_offset;
+ const int64_t i_end = start_offset + length;
+ const int64_t i_last_valid = i_end - 1;
+
+ const int64_t bytes_begin = i_begin / 8;
+ const int64_t bytes_last_valid = i_last_valid / 8;
+
+ if (bytes_begin == bytes_last_valid) {
+ // count bits within a single byte
+ for (int i = 0; i < length; i++) {
+ out[i] = ArrowBitGet(&bits[bytes_begin], i + i_begin % 8);
+ }
+
+ return;
+ }
+
+ // first byte
+ for (int i = 0; i < 8 - (i_begin % 8); i++) {
+ *out++ = ArrowBitGet(&bits[bytes_begin], i + i_begin % 8);
+ }
+
+ // middle bytes
+ for (int64_t i = bytes_begin + 1; i < bytes_last_valid; i++) {
+ _ArrowBitmapUnpackInt8(&bits[i], out);
Review Comment:
```suggestion
_ArrowBitmapUnpackInt8(bits[i], out);
```
##########
src/nanoarrow/buffer_test.cc:
##########
@@ -271,6 +271,65 @@ TEST(BitmapTest, BitmapTestElement) {
EXPECT_EQ(ArrowBitGet(bitmap, 16 + 7), 0);
}
+TEST(BitmapTest, BitmapTestBitsGet) {
+ uint8_t bitmap[10];
+ int8_t result[sizeof(bitmap) * 8];
+
+ memset(bitmap, 0xff, sizeof(bitmap));
+ ArrowBitsGet(bitmap, 0, sizeof(result), result);
+ for (int i = 0; i < sizeof(result); i++) {
+ EXPECT_EQ(result[i], 1);
+ }
+
+ bitmap[2] = 0xfd;
+ ArrowBitsGet(bitmap, 0, sizeof(result), result);
+ EXPECT_EQ(result[16 + 0], 1);
Review Comment:
It's perfect! Thanks! Does it make sense to remove this first bit that
doesn't use the helper? (I am a little confused as to what it's testing that
the tests below it don't cover).
##########
src/nanoarrow/buffer_inline.h:
##########
@@ -222,6 +222,18 @@ static inline int64_t _ArrowBytesForBits(int64_t bits) {
return (bits >> 3) + ((bits & 7) != 0);
}
+static inline void _ArrowBitmapUnpackInt8(const uint8_t* bits, int8_t* out) {
+ const uint8_t word = *bits;
Review Comment:
```suggestion
static inline void _ArrowBitmapUnpackInt8(uint8_t word, int8_t* out) {
```
...may simplify its usage below?
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