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Rev 2243 Rev 2246
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parm [es ax] \
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parm [es ax] \
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modify [ax]
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modify [ax]
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static unsigned long mul16(unsigned short a, unsigned short b);
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#pragma aux mul16 = \
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"mul bx" \
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parm [ax] [bx] \
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value [dx ax]
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/* multiplies two 32 bits number together using 16bit math to avoid
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 * linkage against Watcom libc.
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 * AB * CD = (A*C << 32) + ((B*C + A*D) << 16) + B*D */
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static unsigned long mul32(unsigned long ab, unsigned long cd) {
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  unsigned short a = ab >> 16l;
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  unsigned short b = ab & 0xffff;
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  unsigned short c = cd >> 16l;
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  unsigned short d = cd & 0xffff;
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  unsigned long res;
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  res = mul16(b, c);
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  res += mul16(a, d);
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  res <<= 16;
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  res += mul16(b, d);
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  return(res);
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}
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/* fills freebytes with free bytes for drv (A=0, B=1, etc)
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/* fills freebytes with free bytes for drv (A=0, B=1, etc)
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 * returns DOS ERR code on failure */
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 * returns DOS ERR code on failure */
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static unsigned short cmd_dir_df(unsigned long *freebytes, unsigned char drv) {
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static unsigned short cmd_dir_df(unsigned long *freebytes, unsigned char drv) {
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  unsigned short res = 0;
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  unsigned short res = 0;
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  unsigned short sects_per_clust = 0, avail_clusts = 0, bytes_per_sect = 0;
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  unsigned short sects_per_clust = 0, avail_clusts = 0, bytes_per_sect = 0;
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    pop bx
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    pop bx
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    pop ax
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    pop ax
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  }
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  }
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  /* multiple steps to avoid uint16 overflow */
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  /* multiple steps to avoid uint16 overflow */
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  *freebytes = sects_per_clust;
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  *freebytes = mul32(sects_per_clust, avail_clusts);
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  *freebytes *= avail_clusts;
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  *freebytes *= bytes_per_sect;
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  *freebytes = mul32(*freebytes, bytes_per_sect);
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  return(res);
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  return(res);
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}
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}
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