LAME now calls "sf_command(gs_pSndFileIn, SFC_SET_SCALE_FLOAT_INT_READ, NULL, SF_TRUE)" but it seems that libsndfile reads and decodes an input file during this call (to determine its peak value). Then LAME reads the input file again to encode it to MP3.
IMHO it is better to remove this call and maybe replace sf_read_int(...) with the following:
float insampflt[2 * 1152];
samples_read = sf_read_float(global.snd_file, insampflt, num_channels * samples_to_read);
for(i=0; i<samples_read; i++)
float x = insampflt[i] * ((float)INT_MAX + 1.0);
if (x > (float)INT_MAX) x = (float)INT_MAX;
else if (x < (float)INT_MIN) x = (float)INT_MIN;
insamp[i] = (int)x;
Usually it will result in double conversion (int->float->int) but it is better than reading+decoding an input file twice.