PNG_FP_NEGATIVE  2594 png.c                case 45:  type = PNG_FP_SAW_SIGN + PNG_FP_NEGATIVE; break;
PNG_FP_NEGATIVE  1763 pngpriv.h      #define PNG_FP_NZ_MASK (PNG_FP_SAW_DIGIT | PNG_FP_NEGATIVE | PNG_FP_NONZERO)