diff --git a/pack77.cpp b/pack77.cpp
new file mode 100644
index 0000000..f05555a
--- /dev/null
+++ b/pack77.cpp
@@ -0,0 +1,192 @@
+#include <string.h>
+#include <stdint.h>
+
+#include "text.h"
+
+const char *A0 = " 0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ+-./?";
+const char *A1 = " 0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+const char *A2 = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+const char *A3 = "0123456789";
+const char *A4 = " ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+
+int index(const char *string, char c) {
+    for (int i = 0; *string; ++i, ++string) {
+        if (c == *string) {
+            return i;
+        }
+    }
+    return -1;  // Not found
+}
+
+// Pack a special token, a 22-bit hash code, or a valid base call 
+// into a 28-bit integer.
+int32_t pack28(const char *callsign) {
+    constexpr int32_t NTOKENS = 2063592L;
+    constexpr int32_t MAX22   = 4194304L;
+
+    int length = strlen(callsign);  // We will need it later
+    if (length > 13) return -1;
+
+    // Check for special tokens first
+    if (equals(callsign, "DE")) return 0;
+    if (equals(callsign, "QRZ")) return 1;
+    if (equals(callsign, "CQ")) return 2;
+
+    if (starts_with(callsign, "CQ_")) {
+        int nnum = 0, nlet = 0;
+
+        // if(nnum.eq.3 .and. nlet.eq.0) then n28=3+nqsy
+        // if(nlet.ge.1 .and. nlet.le.4 .and. nnum.eq.0) then n28=3+1000+m
+    }
+
+    // Check for <...> callsign
+    // if(c13(1:1).eq.'<')then
+    //   call save_hash_call(c13,n10,n12,n22)   !Save callsign in hash table
+    //   n28=NTOKENS + n22
+
+    char c6[6] = {' ', ' ', ' ', ' ', ' ', ' '};
+
+    // Work-around for Swaziland prefix:
+    if (starts_with(callsign, "3DA0") && length <= 7) {
+        memcpy(c6, "3D0", 3);
+        memcpy(c6 + 3, callsign + 4, length - 4);
+    }
+    // Work-around for Guinea prefixes:
+    else if (starts_with(callsign, "3X") && is_letter(callsign[2]) && length <= 7) {
+        memcpy(c6, "Q", 1);
+        memcpy(c6 + 1, callsign + 2, length - 2);
+    }
+    else {
+        if (is_digit(callsign[2]) && length <= 6) {
+            memcpy(c6, callsign, length);
+        }
+        else if (is_digit(callsign[1]) && length <= 5) {
+            memcpy(c6 + 1, callsign, length);
+        }
+    }
+
+    // Check for standard callsign
+    int i0, i1, i2, i3, i4, i5;
+    if ((i0 = index(A1, c6[0])) >= 0 && (i1 = index(A2, c6[1])) >= 0 &&
+        (i2 = index(A3, c6[2])) >= 0 && (i3 = index(A4, c6[3])) >= 0 &&
+        (i4 = index(A4, c6[4])) >= 0 && (i5 = index(A4, c6[5])) >= 0) 
+    {
+        // This is a standard callsign
+        int32_t n28 = i0;
+        n28 = n28 * 36 + i1;
+        n28 = n28 * 10 + i2;
+        n28 = n28 * 27 + i3;
+        n28 = n28 * 27 + i4;
+        n28 = n28 * 27 + i5;
+        return NTOKENS + MAX22 + n28;
+    }
+
+    //char c13[13];
+
+    // Treat this as a nonstandard callsign: compute its 22-bit hash
+    // call save_hash_call(c13,n10,n12,n22)   !Save callsign in hash table
+    // n28=NTOKENS + n22
+
+    // n28=iand(n28,ishft(1,28)-1)
+    return -1;
+}
+
+
+// Check if a string could be a valid standard callsign or a valid
+// compound callsign.
+// Return base call "bc" and a logical "cok" indicator.
+bool chkcall(const char *call, char *bc) {
+    int length = strlen(call);   // n1=len_trim(w)
+    if (length > 11) return false;
+    if (0 != strchr(call, '.')) return false;
+    if (0 != strchr(call, '+')) return false;
+    if (0 != strchr(call, '-')) return false;
+    if (0 != strchr(call, '?')) return false;
+    if (length > 6 && 0 != strchr(call, '/')) return false;
+
+  //bc=w(1:6)
+  //i0=index(w,'/')
+  //if(max(i0-1,n1-i0).gt.6) go to 100      !Base call must be < 7 characters
+  //if(i0.ge.2 .and. i0.le.n1-1) then       !Extract base call from compound call
+  //   if(i0-1.le.n1-i0) bc=w(i0+1:n1)//'   '
+  //   if(i0-1.gt.n1-i0) bc=w(1:i0-1)//'   '
+}
+
+
+// Pack Type 1 (Standard 77-bit message) and Type 2 (ditto, with a "/P" call)
+void pack77_1(const char *msg, uint8_t i3, uint8_t *b77) {
+
+    // if(index(w(1),'/P').ge.4 .or. index(w(1),'/R').ge.4) ipa=1
+    // if(index(w(2),'/P').ge.4 .or. index(w(2),'/R').ge.4) ipb=1
+
+    uint32_t n28a, n28b;
+    uint16_t igrid4;
+    
+    n28a <<= 1; // ipa = 0
+    n28b <<= 1; // ipb = 0
+
+    //igrid4 |= 0x8000;   // ir = 1
+
+    // write(c77,1000) n28a,ipa,n28b,ipb,ir,igrid4,i3
+    // 1000 format(2(b28.28,b1),b1,b15.15,b3.3)  
+    // (28 + 1) + (28 + 1) + (1 + 15) + 3  
+
+    b77[0] = (n28a >> 21);
+    b77[1] = (n28a >> 13);
+    b77[2] = (n28a >> 5);
+    b77[3] = (uint8_t)(n28a << 3) | (uint8_t)(n28b >> 26);
+    b77[4] = (n28b >> 18);
+    b77[5] = (n28a >> 10);
+    b77[6] = (n28a >> 2);
+    b77[7] = (uint8_t)(n28a << 6) | (uint8_t)(igrid4 >> 10);
+    b77[8] = (igrid4 >> 2);
+    b77[9] = (uint8_t)(igrid4 << 6) | (uint8_t)(i3 << 3);
+}
+
+
+void packtext77(const char *c13, uint8_t *b71) {
+    // TODO: w=adjustr(c13)
+
+    for (int i = 0; i < 9; ++i) {
+        b71[i] = 0;
+    }
+
+    for (int j = 0; j < 13; ++j) {
+        int q = index(A0, c13[j]);
+
+        // Multiply b71 by 42
+        uint16_t x = 0;
+        for (int i = 8; i >= 0; --i) {
+            x += b71[i] * (uint16_t)42;
+            b71[i] = x;
+            x >>= 8;
+        }
+
+        // Add index of the current char
+        x = (q > 0) ? q : 0;
+        for (int i = 8; i >= 0; --i) {
+            if (x == 0) break;
+            x += b71[i];
+            b71[i] = x;
+            x >>= 8;
+        }
+    }
+}
+
+int pack77(const char *msg, uint8_t *c77) {
+    // Check Type 1 (Standard 77-bit message) or Type 2, with optional "/P"
+    if (starts_with(msg, "CQ ")) {
+        pack77_1(nwords,w,i3,n3,c77);
+        return;
+    }
+    // Check 0.5 (telemetry)
+    // i3=0 n3=5 write(c77,1006) ntel,n3,i3 1006 format(b23.23,2b24.24,2b3.3)
+
+    // Check Type 4 (One nonstandard call and one hashed call)
+    // pack77_4(nwords,w,i3,n3,c77)
+
+    // Default to free text
+    // i3=0 n3=0
+    // packtext77(msg(1:13),c77(1:71))
+    // write(c77(72:77),'(2b3.3)') n3,i3
+}
\ No newline at end of file