// ----------- R_StoreWallRange -----------
// R_FixWiggle(frontsector);
// sectorheight is 144
max_rwscale = 2048<<16 = 134217728

ds_p->scale1 = rw_scale = R_ScaleFromGlobalAngle (viewangle + xtoviewangle[start]);
// ds_p->scale1 = 114623

ds_p->scale2 = R_ScaleFromGlobalAngle (viewangle + xtoviewangle[stop]);
// ds_p->scale2 = 120301273

ds_p->scalestep = rw_scalestep = (ds_p->scale2-rw_scale) / (stop-start);
// stop-start = 1023-265 = 758
// ds_p->scalestep = 158557

// ----------- R_RenderMaskedSegRange() -----------
spryscale = ds->scale1 + (x1 - ds->x1)*rw_scalestep;
// spryscale = 114623 + (265 - 265)*158557 = 114623

for (dcvars.x = x1 ; dcvars.x <= x2 ; dcvars.x++, spryscale += rw_scalestep)
  // dcvars.x from 265 to 1023
  // spryscale starts from 114623, max value is 114623 + (1023-265)*158557 = 120300829

  // sprtopscreen calculation within this loop
  // killough 3/2/98:
  //
  // This calculation used to overflow and cause crashes in Doom:
  //
  // sprtopscreen = centeryfrac - FixedMul(dcvars.texturemid, spryscale);
  //
  // This code fixes it, by using double-precision intermediate
  // arithmetic and by skipping the drawing of 2s normals whose
  // mapping to screen coordinates is totally out of range:
  int_64_t t = ((int_64_t) centeryfrac << FRACBITS) - (int_64_t) dcvars.texturemid * spryscale;
  if (t + (int_64_t) textureheight[texnum] * spryscale < 0 || t > (int_64_t) SCREENHEIGHT << FRACBITS*2)
    continue; // skip if the texture is out of screen's range
  sprtopscreen = (long)(t >> FRACBITS);

  // centeryfrac = 22020096 (336<<16)
  // dcvars.texturemid = 5701632 (87<<16)
  // max value for spryscale is 120300829
  // t = (22020096<<16)-5701632*120300829 = -684467947241472
  // sprtopscreen = t >> FRACBITS = -684467947241472 >> 16 = -10444152027 < MIN_INT
  //
  // first time it overflows when dcvars.x == 422
  // in this case spryscale = 114623 + (422-265)*158557 = 25008072
  // t = (22020096<<16)-5701632*25008072 = -141143714562048
  // sprtopscreen = -141143714562048 >> 16 = -2153682168 < MIN_INT (-2147483647)