mirror of https://gerrit.osmocom.org/libosmocore
add functions for bit-reversal
Sometimes we need stuff like reversing every bit in each byte (but not the byte-order).
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36c5a3e285
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@ -123,6 +123,7 @@ AC_OUTPUT(
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tests/msgfile/Makefile
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tests/ussd/Makefile
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tests/smscb/Makefile
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tests/bits/Makefile
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utils/Makefile
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Doxyfile.core
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Doxyfile.gsm
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@ -46,6 +46,33 @@ int osmo_pbit2ubit_ext(ubit_t *out, unsigned int out_ofs,
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const pbit_t *in, unsigned int in_ofs,
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unsigned int num_bits, int lsb_mode);
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/* BIT REVERSAL */
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/*! \brief bit-reversal mode for osmo_bit_reversal() */
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enum osmo_br_mode {
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/*! \brief reverse all bits in a 32bit dword */
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OSMO_BR_BITS_IN_DWORD = 31,
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/*! \brief reverse byte order in a 32bit dword */
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OSMO_BR_BYTES_IN_DWORD = 24,
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/*! \brief reverse bits of each byte in a 32bit dword */
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OSMO_BR_BITS_IN_BYTE = 7,
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/*! \brief swap the two 16bit words in a 32bit dword */
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OSMO_BR_WORD_SWAP = 16,
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};
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/*! \brief generic bit reversal function */
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uint32_t osmo_bit_reversal(uint32_t x, enum osmo_br_mode k);
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/* \brief reverse the bits within each byte of a 32bit word */
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uint32_t osmo_revbytebits_32(uint32_t x);
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/* \brief reverse the bits within a byte */
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uint32_t osmo_revbytebits_8(uint8_t x);
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/* \brief reverse the bits of each byte in a given buffer */
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void osmo_revbytebits_buf(uint8_t *buf, int len);
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/*! }@ */
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#endif /* _OSMO_BITS_H */
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57
src/bits.c
57
src/bits.c
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@ -128,4 +128,61 @@ int osmo_pbit2ubit_ext(ubit_t *out, unsigned int out_ofs,
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return out_ofs + num_bits;
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}
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/* generalized bit reversal function, Chapter 7 "Hackers Delight" */
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uint32_t osmo_bit_reversal(uint32_t x, enum osmo_br_mode k)
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{
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if (k & 1) x = (x & 0x55555555) << 1 | (x & 0xAAAAAAAA) >> 1;
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if (k & 2) x = (x & 0x33333333) << 2 | (x & 0xCCCCCCCC) >> 2;
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if (k & 4) x = (x & 0x0F0F0F0F) << 4 | (x & 0xF0F0F0F0) >> 4;
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if (k & 8) x = (x & 0x00FF00FF) << 8 | (x & 0xFF00FF00) >> 8;
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if (k & 16) x = (x & 0x0000FFFF) << 16 | (x & 0xFFFF0000) >> 16;
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return x;
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}
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/* generalized bit reversal function, Chapter 7 "Hackers Delight" */
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uint32_t osmo_revbytebits_32(uint32_t x)
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{
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x = (x & 0x55555555) << 1 | (x & 0xAAAAAAAA) >> 1;
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x = (x & 0x33333333) << 2 | (x & 0xCCCCCCCC) >> 2;
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x = (x & 0x0F0F0F0F) << 4 | (x & 0xF0F0F0F0) >> 4;
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return x;
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}
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uint32_t osmo_revbytebits_8(uint8_t x)
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{
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x = (x & 0x55) << 1 | (x & 0xAA) >> 1;
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x = (x & 0x33) << 2 | (x & 0xCC) >> 2;
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x = (x & 0x0F) << 4 | (x & 0xF0) >> 4;
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return x;
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}
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void osmo_revbytebits_buf(uint8_t *buf, int len)
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{
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unsigned int i;
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unsigned int unaligned_cnt;
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int len_remain = len;
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unaligned_cnt = ((unsigned long)buf & 3);
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for (i = 0; i < unaligned_cnt; i++) {
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buf[i] = osmo_revbytebits_8(buf[i]);
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len_remain--;
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if (len_remain <= 0)
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return;
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}
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for (i = unaligned_cnt; i < len; i += 4) {
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uint32_t *cur = (uint32_t *) (buf + i);
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*cur = osmo_revbytebits_32(*cur);
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len_remain -= 4;
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}
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for (i = len - len_remain; i < len; i++) {
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buf[i] = osmo_revbytebits_8(buf[i]);
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len_remain--;
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}
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}
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/*! }@ */
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@ -1,5 +1,5 @@
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if ENABLE_TESTS
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SUBDIRS = timer sms ussd smscb
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SUBDIRS = timer sms ussd smscb bits
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if ENABLE_MSGFILE
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SUBDIRS += msgfile
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endif
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@ -0,0 +1,6 @@
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INCLUDES = $(all_includes) -I$(top_srcdir)/include
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noinst_PROGRAMS = bitrev_test
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bitrev_test_SOURCES = bitrev_test.c
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bitrev_test_LDADD = $(top_builddir)/src/libosmocore.la
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@ -0,0 +1,36 @@
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <string.h>
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#include <osmocom/core/utils.h>
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#include <osmocom/core/bits.h>
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static const uint8_t input[] = { 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80 };
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static const uint8_t exp_out[] = { 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };
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int main(int argc, char **argv)
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{
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uint8_t out[ARRAY_SIZE(input)];
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unsigned int offs;
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for (offs = 0; offs < sizeof(out); offs++) {
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uint8_t *start = out + offs;
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uint8_t len = sizeof(out) - offs;
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memcpy(out, input, sizeof(out));
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printf("INORDER: %s\n", osmo_hexdump(start, len));
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osmo_revbytebits_buf(start, len);
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printf("REVERSED: %s\n", osmo_hexdump(start, len));
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if (memcmp(start, exp_out + offs, len)) {
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printf("EXPECTED: %s\n", osmo_hexdump(exp_out+offs, len));
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fprintf(stderr, "REVERSED != EXPECTED!\n");
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exit(1);
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}
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printf("\n");
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}
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return 0;
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}
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