ubit2pbit flushes at the wrong moment, added one note to bits.h

(e.g. input2[] test sequence from testra/crc_test
 decodes incorrectly to packed bits: 90 b0 3e 80 03 87 53 bd 6f 08,
 this patch fixes it)

2 files changed, 7 insertions, 1 deletions

diff --git a/include/osmocore/bits.h b/include/osmocore/bits.h
index eb2cbcba..8d4a0789 100644
--- a/include/osmocore/bits.h
+++ b/include/osmocore/bits.h
@@ -7,6 +7,12 @@ typedef uint8_t sbit_t;		/* soft bit (-127...127) */
 typedef uint8_t ubit_t;		/* unpacked bit (0 or 1) */
 typedef uint8_t pbit_t;		/* packed bis (8 bits in a byte) */
 
+/*
+   NOTE on the endianess of pbit_t:
+   Bits in a pbit_t are ordered MSB first, i.e. 0x80 is the first bit.
+   Bit i in a pbit_t array is array[i/8] & (1<<(7-i%8))
+*/
+
 /* determine how many bytes we would need for 'num_bits' packed bits */
 static inline unsigned int osmo_pbit_bytesize(unsigned int num_bits)
 {
diff --git a/src/bits.c b/src/bits.c
index 029cfe55..fcdf5cc3 100644
--- a/src/bits.c
+++ b/src/bits.c
@@ -15,7 +15,7 @@ int osmo_ubit2pbit(pbit_t *out, const ubit_t *in, unsigned int num_bits)
 
 		curbyte |= (in[i] << bitnum);
 
-		if (i > 0 && i % 8 == 0) {
+		if(i % 8 == 7){
 			*outptr++ = curbyte;
 			curbyte = 0;
 		}