libavcodec/pngdec.c:219: error: Uninitialized Value
  The value read from b was never initialized.

libavcodec/pngdec.c:219:9: 
217.         }
218. #define OP_AVG(x,s,l) (((x + l) >> 1) + s) & 0xff
219.         UNROLL_FILTER(OP_AVG);
             ^
220.         break;
221.     case PNG_FILTER_VALUE_PAETH:

static void png_filter_row(DSPContext *dsp, uint8_t *dst, int filter_type,
                           uint8_t *src, uint8_t *last, int size, int bpp)
{
    int i, p, r, g, b, a;
    switch(filter_type) {
    case PNG_FILTER_VALUE_NONE:
        memcpy(dst, src, size);
        break;
    case PNG_FILTER_VALUE_SUB:
        for(i = 0; i < bpp; i++) {
            dst[i] = src[i];
        }
        if(bpp == 4) {
            p = *(int*)dst;
            for(; i < size; i+=bpp) {
                int s = *(int*)(src+i);
                p = ((s&0x7f7f7f7f) + (p&0x7f7f7f7f)) ^ ((s^p)&0x80808080);
                *(int*)(dst+i) = p;
            }
        } else {
#define OP_SUB(x,s,l) x+s
            UNROLL_FILTER(OP_SUB);
        }
        break;
    case PNG_FILTER_VALUE_UP:
        dsp->add_bytes_l2(dst, src, last, size);
        break;
    case PNG_FILTER_VALUE_AVG:
        for(i = 0; i < bpp; i++) {
            p = (last[i] >> 1);
            dst[i] = p + src[i];
        }
#define OP_AVG(x,s,l) (((x + l) >> 1) + s) & 0xff
        UNROLL_FILTER(OP_AVG);
        break;
    case PNG_FILTER_VALUE_PAETH:
        for(i = 0; i < bpp; i++) {
            p = last[i];
            dst[i] = p + src[i];
        }
        if(bpp > 1 && size > 4) {
            int w = bpp==4 ? size : size-3;
            dsp->add_png_paeth_prediction(dst+i, src+i, last+i, w-i, bpp);
            i = w;
        }
        ff_add_png_paeth_prediction(dst+i, src+i, last+i, size-i, bpp);
        break;
    }
}
['static void png_filter_row(DSPContext *dsp, uint8_t *dst, int filter_type,\n                           uint8_t *src, uint8_t *last, int size, int bpp)\n{\n    int i, p, r, g, b, a;\n    switch(filter_type) {\n    case PNG_FILTER_VALUE_NONE:\n        memcpy(dst, src, size);\n        break;\n    case PNG_FILTER_VALUE_SUB:\n        for(i = 0; i < bpp; i++) {\n            dst[i] = src[i];\n        }\n        if(bpp == 4) {\n            p = *(int*)dst;\n            for(; i < size; i+=bpp) {\n                int s = *(int*)(src+i);\n                p = ((s&0x7f7f7f7f) + (p&0x7f7f7f7f)) ^ ((s^p)&0x80808080);\n                *(int*)(dst+i) = p;\n            }\n        } else {\n#define OP_SUB(x,s,l) x+s\n            UNROLL_FILTER(OP_SUB);\n        }\n        break;\n    case PNG_FILTER_VALUE_UP:\n        dsp->add_bytes_l2(dst, src, last, size);\n        break;\n    case PNG_FILTER_VALUE_AVG:\n        for(i = 0; i < bpp; i++) {\n            p = (last[i] >> 1);\n            dst[i] = p + src[i];\n        }\n#define OP_AVG(x,s,l) (((x + l) >> 1) + s) & 0xff\n        UNROLL_FILTER(OP_AVG);\n        break;\n    case PNG_FILTER_VALUE_PAETH:\n        for(i = 0; i < bpp; i++) {\n            p = last[i];\n            dst[i] = p + src[i];\n        }\n        if(bpp > 1 && size > 4) {\n            int w = bpp==4 ? size : size-3;\n            dsp->add_png_paeth_prediction(dst+i, src+i, last+i, w-i, bpp);\n            i = w;\n        }\n        ff_add_png_paeth_prediction(dst+i, src+i, last+i, size-i, bpp);\n        break;\n    }\n}']