add functions for bit-reversal
Sometimes we need stuff like reversing every bit in each byte (but not
the byte-order).
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--;
+ }
+}
+
/*! }@ */