How to translate this C macro to D mixin/template mixin?

[VitaliiY]

Could anybody help with translation of this C macro to D 
mixin/mixin template? Here a - unsigned char, b - int. It's 
simple with STARTDATA as mixin, but STOREBITS and ADDBITS use 
variables defined in STARTDATA scope, so I can't understand how 
to do mixin template with it.

     #define STARTDATA \
       size_t ressize=0; \
       char *blockstart; \
       int numbits; \
       uint64_t bitbuffer=0;

     #define STOREBITS \
       while(numbits >= 8) \
       { \
         if(!size) return 0; \
         *(buffer++) = bitbuffer>>(numbits-8); \
         numbits -= 8; \
         ++ressize; \
         --size; \
       }

     #define ADDBITS(a, b) \
       { \
         bitbuffer = (bitbuffer<<(a))|((b)&((1<<a)-1)); \
         numbits += (a); \
         STOREBITS \
       }