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Diffstat (limited to 'jpegdec/jpegdec.c')
| -rw-r--r-- | jpegdec/jpegdec.c | 179 |
1 files changed, 179 insertions, 0 deletions
diff --git a/jpegdec/jpegdec.c b/jpegdec/jpegdec.c new file mode 100644 index 0000000..b7b4cf6 --- /dev/null +++ b/jpegdec/jpegdec.c @@ -0,0 +1,179 @@ +// ================================================================================================ +// Basic JPEG decoder. Does no bounds checking on inputs. +// +// ref: https://en.wikipedia.org/wiki/JPEG#Syntax_and_structure +// ref: ITU-T T.81 (1992) — ISO/IEC 10918-1:1994 +// +// Test files: +// $ ffmpeg -f lavfi -i testsrc=size=800x600:rate=1 -frames:v 1 test.jpg +// +// Changelog: +// ??/??/2026: Initial release +// +// License: +// Copyright (c) 2026 Hunter Kvalevog +// +// Permission to use, copy, modify, and/or distribute this software for any +// purpose with or without fee is hereby granted. +// +// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES +// WITH REGARD TO THIS SOFTWARE. +// ================================================================================================ + +#include <assert.h> +#include <stdbool.h> +#include <stdint.h> +#include <stdio.h> +#include <stdlib.h> + +// Marker codes - Table B.1 +enum +{ + MC_SOF0 = 0xC0, + MC_SOF1 = 0xC1, + MC_SOF2 = 0xC2, + MC_SOF3 = 0xC3, + MC_SOF5 = 0xC5, + MC_SOF6 = 0xC6, + MC_SOF7 = 0xC7, + MC_SOF8 = 0xC8, + MC_SOF9 = 0xC9, + MC_SOFA = 0xCA, + MC_SOFB = 0xCB, + MC_SOFC = 0xCC, + MC_SOFD = 0xCD, + MC_SOFE = 0xCE, + MC_DHT = 0xC4, + MC_DAC = 0xCC, + MC_RST0 = 0xD0, + MC_RST1 = 0xD1, + MC_RST2 = 0xD2, + MC_RST3 = 0xD3, + MC_RST4 = 0xD4, + MC_RST5 = 0xD5, + MC_RST6 = 0xD6, + MC_RST7 = 0xD7, + MC_SOI = 0xD8, + MC_EOI = 0xD9, + MC_SOS = 0xDA, + MC_DQT = 0xDB, + MC_DNL = 0xDC, + MC_DRI = 0xFF, + MC_DHP = 0xDE, + MC_EXP = 0xDF, + MC_APP0 = 0xE0, + MC_APP1 = 0xE1, + MC_APP2 = 0xE2, + MC_APP3 = 0xE3, + MC_APP4 = 0xE4, + MC_APP5 = 0xE5, + MC_APP6 = 0xE6, + MC_APP7 = 0xE7, + MC_APP8 = 0xE8, + MC_APP9 = 0xE9, + MC_APPA = 0xEA, + MC_APPB = 0xEB, + MC_APPC = 0xEC, + MC_APPD = 0xED, + MC_APPE = 0xEE, + MC_APPF = 0xEF, + MC_COM = 0xFE, +}; + +int main(int argc, const char **argv) +{ + uint8_t *bbuf = 0; + size_t blen = 0; + { + if (argc != 2) { + printf("Supply a file\n"); + return 0; + } + FILE *fp = fopen(argv[1], "rb"); + if (!fp) { + perror("Couldn't open file"); + } + + fseek(fp, 0, SEEK_END); + blen = ftell(fp); + fseek(fp, 0, SEEK_SET); + + bbuf = malloc(blen); + fread(bbuf, 1, blen, fp); + + fclose(fp); + } + + const uint8_t *pbuf = bbuf; + + // File should start with SOI + assert(pbuf[0] == 0xFF && pbuf[1] == MC_SOI && "not a jpeg"); + pbuf += 2; + + #define READ_LEN() ((pbuf[0] << 8) | pbuf[1]) + + while (true) { + uint8_t mc0 = pbuf[0]; + uint8_t mc1 = pbuf[1]; + pbuf += 2; + assert(mc0 == 0xFF); + switch (mc1) { + case MC_APP0: + case MC_APP1: + case MC_APP2: + case MC_APP3: + case MC_APP4: + case MC_APP5: + case MC_APP6: + case MC_APP7: + case MC_APP8: + case MC_APP9: + case MC_APPA: + case MC_APPB: + case MC_APPC: + case MC_APPD: + case MC_APPE: + case MC_APPF: { + printf("MC_APP%d\n", mc1 & 0xF); + uint16_t len = READ_LEN(); + pbuf += len; + } break; + case MC_COM: { + printf("MC_COM\n"); + uint16_t len = READ_LEN(); + pbuf += len; + } break; + case MC_DHT: { + printf("MC_DHT\n"); + uint16_t len = READ_LEN(); + pbuf += len; + } break; + case MC_DQT: { + printf("MC_DQT\n"); + uint16_t len = READ_LEN(); + pbuf += len; + } break; + case MC_SOF0: { + printf("MC_SOF0 (Baseline DCT)\n"); + uint16_t len = READ_LEN(); + pbuf += len; + } break; + case MC_SOF2: { + printf("MC_SOF2 (Progressive DCT)\n"); + uint16_t len = READ_LEN(); + pbuf += len; + } break; + case MC_SOS: { + // Section B.2.3 + printf("MC_SOS\n"); + uint16_t len = READ_LEN(); + pbuf += len; + } break; + default: { + printf("Got unknown marker code 0x%X\n", mc1); + exit(1); + } break; + } + } +} + |