lib: Add buffer truncate

diff --git a/src/lib/buffer.c b/src/lib/buffer.c
index 4bcd91261cf91c234ea4741d789607d609110258..61428160ad182b1a2afcab5b6d5fd28398817899 100644 (file)
--- a/src/lib/buffer.c
+++ b/src/lib/buffer.c
@@ -358,3 +358,28 @@ void buffer_verify_pool(buffer_t *_buf)
                i_assert(ret == buf->w_buffer);
        }
 }
+
+void buffer_truncate_rshift_bits(buffer_t *buf, size_t bits)
+{
+       /* no-op if it's shorten than bits in any case.. */
+       if (buf->used * 8 < bits) return;
+
+       if (bits > 0) {
+               /* truncate it to closest byte boundary */
+               size_t bytes = ((bits + 7) & -8U)/8;
+               /* remainding bits */
+               bits = bits % 8;
+               buffer_set_used_size(buf, I_MIN(bytes, buf->used));
+               unsigned char *ptr = buffer_get_modifiable_data(buf, &bytes);
+               /* right shift over byte array */
+               if (bits > 0) {
+                       for(size_t i=bytes-1;i>0;i--)
+                               ptr[i] = (ptr[i]>>(8-bits)) +
+                                        ((ptr[i-1]&(0xff>>(bits)))<<bits);
+                       ptr[0] = ptr[0]>>(8-bits);
+               }
+       } else {
+               buffer_set_used_size(buf, 0);
+       }
+}
+

diff --git a/src/lib/buffer.h b/src/lib/buffer.h
index 723c79a4a0acf8c0a2f4541a8b97c58b7cc9fb8c..1d38d1efbec10f904b341a1d2ebb4c9abf21c811 100644 (file)
--- a/src/lib/buffer.h
+++ b/src/lib/buffer.h
@@ -121,4 +121,29 @@ buffer_get_used_size(const buffer_t *buf)
    buffer needs to be increased. */
 void buffer_verify_pool(buffer_t *buf);
 
+/* This will truncate your byte buffer to contain at most
+   given number of bits. 
+
+ 1 bits:    01 00000001
+ 2 bits:    03 00000011
+ 3 bits:    07 00000111
+ 4 bits:    0f 00001111
+ 5 bits:    1f 00011111
+ 6 bits:    3f 00111111
+ 7 bits:    7f 01111111
+ 8 bits:    ff 11111111
+ 9 bits:  01ff 0000000111111111
+10 bits:  03ff 0000001111111111
+11 bits:  07ff 0000011111111111
+12 bits:  0fff 0000111111111111
+13 bits:  1fff 0001111111111111
+14 bits:  3fff 0011111111111111
+15 bits:  7fff 0111111111111111
+16 bits:  ffff 1111111111111111
+
+ and so forth
+
+*/
+void buffer_truncate_rshift_bits(buffer_t *buf, size_t bits);
+
 #endif