add functions for bit-reversal
Sometimes we need stuff like reversing every bit in each byte (but not
the byte-order).
diff --git a/configure.ac b/configure.ac
index ef4b0aa..f624f2a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -123,6 +123,7 @@
tests/msgfile/Makefile
tests/ussd/Makefile
tests/smscb/Makefile
+ tests/bits/Makefile
utils/Makefile
Doxyfile.core
Doxyfile.gsm
diff --git a/include/osmocom/core/bits.h b/include/osmocom/core/bits.h
index ab4cf77..b541b9c 100644
--- a/include/osmocom/core/bits.h
+++ b/include/osmocom/core/bits.h
@@ -46,6 +46,33 @@
const pbit_t *in, unsigned int in_ofs,
unsigned int num_bits, int lsb_mode);
+
+/* BIT REVERSAL */
+
+/*! \brief bit-reversal mode for osmo_bit_reversal() */
+enum osmo_br_mode {
+ /*! \brief reverse all bits in a 32bit dword */
+ OSMO_BR_BITS_IN_DWORD = 31,
+ /*! \brief reverse byte order in a 32bit dword */
+ OSMO_BR_BYTES_IN_DWORD = 24,
+ /*! \brief reverse bits of each byte in a 32bit dword */
+ OSMO_BR_BITS_IN_BYTE = 7,
+ /*! \brief swap the two 16bit words in a 32bit dword */
+ OSMO_BR_WORD_SWAP = 16,
+};
+
+/*! \brief generic bit reversal function */
+uint32_t osmo_bit_reversal(uint32_t x, enum osmo_br_mode k);
+
+/* \brief reverse the bits within each byte of a 32bit word */
+uint32_t osmo_revbytebits_32(uint32_t x);
+
+/* \brief reverse the bits within a byte */
+uint32_t osmo_revbytebits_8(uint8_t x);
+
+/* \brief reverse the bits of each byte in a given buffer */
+void osmo_revbytebits_buf(uint8_t *buf, int len);
+
/*! }@ */
#endif /* _OSMO_BITS_H */
diff --git a/src/bits.c b/src/bits.c
index 3955e3b..9eb2d69 100644
--- a/src/bits.c
+++ b/src/bits.c
@@ -128,4 +128,61 @@
return out_ofs + num_bits;
}
+/* generalized bit reversal function, Chapter 7 "Hackers Delight" */
+uint32_t osmo_bit_reversal(uint32_t x, enum osmo_br_mode k)
+{
+ if (k & 1) x = (x & 0x55555555) << 1 | (x & 0xAAAAAAAA) >> 1;
+ if (k & 2) x = (x & 0x33333333) << 2 | (x & 0xCCCCCCCC) >> 2;
+ if (k & 4) x = (x & 0x0F0F0F0F) << 4 | (x & 0xF0F0F0F0) >> 4;
+ if (k & 8) x = (x & 0x00FF00FF) << 8 | (x & 0xFF00FF00) >> 8;
+ if (k & 16) x = (x & 0x0000FFFF) << 16 | (x & 0xFFFF0000) >> 16;
+
+ return x;
+}
+
+/* generalized bit reversal function, Chapter 7 "Hackers Delight" */
+uint32_t osmo_revbytebits_32(uint32_t x)
+{
+ x = (x & 0x55555555) << 1 | (x & 0xAAAAAAAA) >> 1;
+ x = (x & 0x33333333) << 2 | (x & 0xCCCCCCCC) >> 2;
+ x = (x & 0x0F0F0F0F) << 4 | (x & 0xF0F0F0F0) >> 4;
+
+ return x;
+}
+
+uint32_t osmo_revbytebits_8(uint8_t x)
+{
+ x = (x & 0x55) << 1 | (x & 0xAA) >> 1;
+ x = (x & 0x33) << 2 | (x & 0xCC) >> 2;
+ x = (x & 0x0F) << 4 | (x & 0xF0) >> 4;
+
+ return x;
+}
+
+void osmo_revbytebits_buf(uint8_t *buf, int len)
+{
+ unsigned int i;
+ unsigned int unaligned_cnt;
+ int len_remain = len;
+
+ unaligned_cnt = ((unsigned long)buf & 3);
+ for (i = 0; i < unaligned_cnt; i++) {
+ buf[i] = osmo_revbytebits_8(buf[i]);
+ len_remain--;
+ if (len_remain <= 0)
+ return;
+ }
+
+ for (i = unaligned_cnt; i < len; i += 4) {
+ uint32_t *cur = (uint32_t *) (buf + i);
+ *cur = osmo_revbytebits_32(*cur);
+ len_remain -= 4;
+ }
+
+ for (i = len - len_remain; i < len; i++) {
+ buf[i] = osmo_revbytebits_8(buf[i]);
+ len_remain--;
+ }
+}
+
/*! }@ */
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 2b4ac6e..6c3cb33 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -1,5 +1,5 @@
if ENABLE_TESTS
-SUBDIRS = timer sms ussd smscb
+SUBDIRS = timer sms ussd smscb bits
if ENABLE_MSGFILE
SUBDIRS += msgfile
endif
diff --git a/tests/bits/Makefile.am b/tests/bits/Makefile.am
new file mode 100644
index 0000000..dd03e83
--- /dev/null
+++ b/tests/bits/Makefile.am
@@ -0,0 +1,6 @@
+INCLUDES = $(all_includes) -I$(top_srcdir)/include
+noinst_PROGRAMS = bitrev_test
+
+bitrev_test_SOURCES = bitrev_test.c
+bitrev_test_LDADD = $(top_builddir)/src/libosmocore.la
+
diff --git a/tests/bits/bitrev_test.c b/tests/bits/bitrev_test.c
new file mode 100644
index 0000000..5eca990
--- /dev/null
+++ b/tests/bits/bitrev_test.c
@@ -0,0 +1,36 @@
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+#include <osmocom/core/utils.h>
+#include <osmocom/core/bits.h>
+
+static const uint8_t input[] = { 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80 };
+static const uint8_t exp_out[] = { 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };
+
+int main(int argc, char **argv)
+{
+ uint8_t out[ARRAY_SIZE(input)];
+ unsigned int offs;
+
+ for (offs = 0; offs < sizeof(out); offs++) {
+ uint8_t *start = out + offs;
+ uint8_t len = sizeof(out) - offs;
+
+ memcpy(out, input, sizeof(out));
+
+ printf("INORDER: %s\n", osmo_hexdump(start, len));
+ osmo_revbytebits_buf(start, len);
+ printf("REVERSED: %s\n", osmo_hexdump(start, len));
+ if (memcmp(start, exp_out + offs, len)) {
+ printf("EXPECTED: %s\n", osmo_hexdump(exp_out+offs, len));
+ fprintf(stderr, "REVERSED != EXPECTED!\n");
+ exit(1);
+ }
+ printf("\n");
+ }
+
+ return 0;
+}