Today's submitter goes by "[object Object]", which I appreciate the JavaScript gag even when they send us C code.
This particular bit of C code exists to help output data in fixed-width files. What you run into, with fixed-width files, is that it becomes very important to properly pad all your columns. It's not a difficult programming challenge, but it's also easy to make mistakes that cause hard-to-spot bugs. And given that most systems using fixed-width files are legacy systems with their own idiosyncrasies, things could easily go wrong.
Things go more wrong when you don't actually know the right way to pad strings. Thus this excerpt from constants.h.
    #define LABEL_SIZE1                  1
    #define LABEL_SIZE2                  2
    #define LABEL_SIZE3                  3
    #define LABEL_SIZE4                  4
    #define LABEL_SIZE5                  5
    #define LABEL_SIZE6                  6
    #define LABEL_SIZE7                  7
    #define LABEL_SIZE8                  8
    #define LABEL_SIZE9                  9
    #define LABEL_SIZE10                 10
    #define LABEL_SIZE11                 11
    #define LABEL_SIZE12                 12
    #define LABEL_SIZE14                 14
    #define LABEL_SIZE15                 15
    #define LABEL_SIZE16                 16
    #define LABEL_SIZE21                 21
    #define LABEL_SIZE20                 20
    #define LABEL_SIZE23                 23
    #define LABEL_SIZE24                 24
    #define LABEL_SIZE25                 25
    #define LABEL_SIZE30                 30
    #define LABEL_SIZE31                 31
    #define LABEL_SIZE32                 32
    #define LABEL_SIZE33                 33
    #define LABEL_SIZE37                 37
    #define LABEL_SIZE39                 39
    #define LABEL_SIZE40                 40
    #define LABEL_SIZE43                 43
    #define LABEL_SIZE45                 45
    #define LABEL_SIZE48                 48
    #define LABEL_SIZE50                 50
    #define LABEL_SIZE53                 53
    #define LABEL_SIZE73                 73
    #define LABEL_SIZE80                 80
    #define LABEL_SIZE121                121
    #define LABEL_SIZE100                100
    #define LABEL_SIZE149                149
    #define LABEL_SIZE150                150
    #define LABEL_SIZE170                170
    #define LABEL_SIZE175                175
    #define LABEL_SIZE205                205
    #define LABEL_SIZE208                208
    #define LABEL_SIZE723                723
    #define LABEL_SIZE725                725
    #define LABEL_SIZE753                753
    #define LABEL_SIZE825                825
    #define LABEL_SIZE853                853
    #define SPACE_1                      " "
    #define SPACE_2                      "  "
    #define SPACE_3                      "   "
    #define SPACE_4                      "    "
    #define SPACE_5                      "     "
    #define SPACE_8                      "        "
    #define SPACE_10                     "          "
    #define SPACE_11                     "           "
    #define SPACE_12                     "            "
    #define SPACE_13                     "             "
    #define SPACE_14                     "              "
    #define SPACE_15                     "               "
    #define SPACE_19                     "                   "
    #define SPACE_20                     "                    "
    #define SPACE_21                     "                     "
    #define SPACE_23                     "                       "
    #define SPACE_25                     "                         "
    #define SPACE_29                     "                             "
    #define SPACE_30                     "                              "
    #define SPACE_31                     "                               "
    #define SPACE_32                     "                                "
    #define SPACE_37                     "                                     "
    #define SPACE_39                     "                                       "
    #define SPACE_41                     "                                         "
    #define SPACE_53                     "                                                     "
    #define SPACE_57                     "                                                         "
    #define ZERO_1                       "0"
    #define ZERO_2                       "00"
    #define ZERO_3                       "000"
    #define ZERO_4                       "0000"
    #define ZERO_5                       "00000"
    #define ZERO_8                       "00000000"
    #define ZERO_10                      "0000000000"
    #define ZERO_11                      "00000000000"
    #define ZERO_14                      "00000000000000"
    #define ZERO_29                      "00000000000000000000000000000"
    #define NINE_11                      "99999999999"
    #define NINE_29                      "99999999999999999999999999999"
    // Min max values
    #define MIN_MINUS1                   -1
    #define MIN_0                        0
    #define MIN_1                        1
    #define MIN_111                      111
    #define MAX_0                        0
    #define MAX_1                        1
    #define MAX_2                        2
    #define MAX_3                        3
    #define MAX_4                        4
    #define MAX_7                        7
    #define MAX_9                        9
    #define MAX_12                       12
    #define MAX_15                       15
    #define MAX_63                       63
    #define MAX_99                       99
    #define MAX_114                      114
    #define MAX_127                      127
    #define MAX_255                      255
    #define MAX_256                      256
    #define MAX_999                      999
    #define MAX_1023                     1023
    #define MAX_4095                     4095
    #define MAX_9999                     9999
    #define MAX_16383                    16383
    #define MAX_65535                    65535
    #define MAX_9_5                      99999
    #define MAX_9_6                      999999
    #define MAX_9_7                      9999999
    #define MAX_9_8                      99999999
    #define MAX_9_9                      999999999
    #define MAX_9_10                     9999999999
    #define MAX_9_11                     99999999999
The full file is 500 lines long, all in this pattern. It's also delightfully meta: these constants are used for generating fixed-width files, and this file is itself a fixed-width file, thanks to the developer wearing their tab key out.