PNG_FP_NEGATIVE  1334 3rdparty/libpng/png.c       case 45:  type = PNG_FP_SAW_SIGN + PNG_FP_NEGATIVE; break;
PNG_FP_NEGATIVE  1577 3rdparty/libpng/pngpriv.h #define PNG_FP_NZ_MASK (PNG_FP_SAW_DIGIT | PNG_FP_NEGATIVE | PNG_FP_NONZERO)