asm.txt

// for more details see
// https://dhconnelly.com/advent-of-code-2019-commentary.html#intcode-reverse-engineering

// set the stack pointer to after the program data
[   0]   adjrel    imm(424)

// call procedure C with ret=11 and arg0=X
// halt if X < 0
[   2]     read      rel(1)
[   4]      mul     imm(11)   imm(1)   rel(0)
[   8]   jmpnot      imm(0) imm(282)

// call procedure B with ret=18 and arg0=X
// 221 <- abs(X)
[  11]      add     imm(18)   imm(0)   rel(0)
[  15]   jmpnot      imm(0) imm(259)
[  18]      add      imm(0)   rel(1) pos(221)

// call procedure C with ret=31 and arg0=Y
// halt if Y < 0
[  22]     read      rel(1)
[  24]      mul     imm(31)   imm(1)   rel(0)
[  28]   jmpnot      imm(0) imm(282)

// call procedure B with ret=38 and arg0=Y
// Y = abs(Y)
[  31]      mul      imm(1)  imm(38)   rel(0)
[  35]    jmpif      imm(1) imm(259)

// call procedure D with ret=57 and arg0=1, arg1=1, arg2=abs(Y)
// because pos(23) = 1
// = Y
// 222 <- Y
[  38]      mul      imm(1)  pos(23)   rel(2)
[  42]      add      imm(0)   rel(1)   rel(3)
[  46]      add      imm(0)   imm(1)   rel(1)
[  50]      add      imm(0)  imm(57)   rel(0)
[  54]   jmpnot      imm(0) imm(303)
[  57]      mul      rel(1)   imm(1) pos(222)

// call procedure A with ret=80 and arg0=259, arg1=X, arg2=X, arg3=X
// = 259(X, X, X) = abs(X)
[  61]      add    pos(221)   imm(0)   rel(3)
[  65]      mul      imm(1) pos(221)   rel(2)
[  69]      mul    imm(259)   imm(1)   rel(1)
[  73]      add     imm(80)   imm(0)   rel(0)
[  77]    jmpif      imm(1) imm(225)

// call procedure D with ret=91 and arg0=X, arg1=149, arg2=X
// = 149x^2
// -> 223
[  80]      mul      imm(1) imm(149)   rel(2)
[  84]      add      imm(0)  imm(91)   rel(0)
[  88]    jmpif      imm(1) imm(303)
[  91]      mul      rel(1)   imm(1) pos(223)

// call procedure A
// with ret=118, arg0=225, arg1=225, arg2=259, arg3=^
// call A(A, A, B, Y)
// = A(A, B, Y)
// = A(B, Y)
// = B(Y)
// = abs(Y)
[  95]      mul    pos(222)   imm(1)   rel(4)
[  99]      mul    imm(259)   imm(1)   rel(3)
[ 103]      mul    imm(225)   imm(1)   rel(2)
[ 107]      mul    imm(225)   imm(1)   rel(1)
[ 111]      add    imm(118)   imm(0)   rel(0)
[ 115]    jmpif      imm(1) imm(225)

// call D with ret=133 and Y, 127, Y
// = 127y^2
[ 118]      mul      imm(1) pos(222)   rel(3)
[ 122]      add      imm(0) imm(127)   rel(2)
[ 126]      mul    imm(133)   imm(1)   rel(0)
[ 130]    jmpif      imm(1) imm(303)

// x0 = -above = -127y^2
// += 149x^2
// 223 <- 149x^2 - 127y^2
[ 133]      mul      rel(1)  imm(-1)   rel(1)
[ 137]      add    pos(223)   rel(1)   rel(1)
[ 141]      mul      imm(1) imm(148)   rel(0)
[ 145]   jmpnot      imm(0) imm(259)
[ 148]      add      rel(1)   imm(0) pos(223)

// call A with ret=195 and arg0=303, arg1=14, arg2=Y, arg3=X
// = D(14, Y, X)
// rel(4) = X
// = 14yx
[ 152]      add    pos(221)   imm(0)   rel(4)
// rel(3) = Y
[ 156]      mul    pos(222)   imm(1)   rel(3)
// rel(2) = 14
[ 160]      mul     imm(14)   imm(1)   rel(2)
// *224 <- *303-2 = 301
[ 164]      add    pos(132)  imm(-2) pos(224)
// *224 <- *224 * 2 = 602
[ 168]      mul    pos(224)   imm(2) pos(224)
// *224 <- *224 + 3 = 605
[ 172]      add    pos(224)   imm(3) pos(224)
// *132 <- *132 * -1 = -303
[ 176]      mul    pos(132)  imm(-1) pos(132)
// *224 <- *224 + *132 = 605 - 303 = 302
[ 180]      add    pos(224) pos(132) pos(224)
// rel(1) = *224 + 1 = 303
[ 184]      add    pos(224)   imm(1)   rel(1)
// rel(0) = 195
[ 188]      add    imm(195)   imm(0)   rel(0)
[ 192]   jmpnot      imm(0) pos(108)

// call D with ret=214 and arg0=1, arg1=(14yx < 149x^2-127y^2), arg2=-1
[ 195]       lt      rel(1) pos(223)   rel(2)
[ 199]      mul      imm(1)  pos(23)   rel(1)
[ 203]      add      imm(0)  imm(-1)   rel(3)
[ 207]      mul    imm(214)   imm(1)   rel(0)
[ 211]   jmpnot      imm(0) imm(303)
// maybe |149x^2-127y^2| < 14yx ?

// print ret+1
[ 214]      add      imm(1)   rel(1)   rel(1)
[ 218]    print      rel(1)
[ 220]     halt    

// data section for the above
[ 221] [0] // X
[ 222] [0] // Y
[ 223] [0] // 149x^2 if x < 149 then 149x^2 - 127y^2
[ 224] [0] // 127y^2 if y < 127 then scratch

// calling convention for procedure with N parameters:
// push ret and arguments 1..N onto the stack, in that order.
// retrieve return value from rel+1

// procedure will move stack pointer forward by N+K, where
// K is the number of locals to be used, then pop the stack
// by moving it back by N+K and jump to rel(=ret). the return
// value will be at rel+1.

// ==========================================================
// procedure A (4 params):
// pos(249) <- arg0
// push arg1
// push arg2
// push arg3
// call procedure arg0 with ret=250, arg1, arg2, arg3
// return the return value
// =>
// return arg0(arg1, arg2, arg3) 
[ 225]   adjrel      imm(5)
[ 227]      mul     rel(-4)   imm(1) pos(249)
[ 231]      mul      imm(1)  rel(-3)   rel(1)
[ 235]      add     rel(-2)   imm(0)   rel(2)
[ 239]      add     rel(-1)   imm(0)   rel(3)
[ 243]      mul      imm(1) imm(250)   rel(0)
[ 247]    jmpif      imm(1) imm(225) // 225 -> arg0, see above
[ 250]      mul      imm(1)   rel(1)  rel(-4)
[ 254]   adjrel     imm(-5)
[ 256]   jmpnot      imm(0)   rel(0)

// ==========================================================
// procedure B (1 params, 1 local):
// x0 = 2 * (arg0 > 0 ? 1 : 0) - 1
// return x0 * arg0
// =>
// return abs(arg0)
[ 259]   adjrel      imm(3)
[ 261]       lt      imm(0)  rel(-2)  rel(-1)
[ 265]      mul     rel(-1)   imm(2)  rel(-1)
[ 269]      add     rel(-1)  imm(-1)  rel(-1)
[ 273]      mul     rel(-1)  rel(-2)  rel(-2)
[ 277]   adjrel     imm(-3)
[ 279]    jmpif      imm(1)   rel(0)

// ==========================================================
// procedure C:
// x0 = arg0 < 0
// if !x0: goto 294
// print(0)
// halt
// 294: arg0 *= 1
// return
// =>
// if x0 < 0:
//   print(0)
//   halt
// return x0
[ 282]   adjrel      imm(3)
[ 284]       lt     rel(-2)   imm(0)  rel(-1)
[ 288]   jmpnot     rel(-1) imm(294)
[ 291]    print      imm(0)
[ 293]     halt    
[ 294]      mul     rel(-2)   imm(1)  rel(-2)
[ 298]   adjrel     imm(-3)
[ 300]   jmpnot      imm(0)   rel(0)

// procedure D (3 params, 1 local):
// arg0, arg1, arg2:
// if 
// if arg1 >= arg0:
//   goto 346
[ 303]   adjrel      imm(5)
[ 305]       lt     rel(-3)  rel(-4)  rel(-1)
[ 309]   jmpnot     rel(-1) imm(346)
// if arg0 > arg1:
[ 312]      add     rel(-4)  rel(-3)  rel(-4)
[ 316]      mul     rel(-3)  imm(-1)  rel(-1)
[ 320]      add     rel(-4)  rel(-1)   rel(2)
[ 324]      mul      rel(2)  imm(-1)  rel(-1)
[ 328]      add     rel(-4)  rel(-1)   rel(1)
[ 332]      add      imm(0)  rel(-2)   rel(3)
[ 336]      add    imm(343)   imm(0)   rel(0)
[ 340]   jmpnot      imm(0) imm(303)
[ 343]   jmpnot      imm(0) imm(415)

// if arg0 <= arg1

// x0 = arg2 < arg1
// if !x0: goto 387
// => if arg1 <= arg2: goto 387
[ 346]       lt     rel(-2)  rel(-3)  rel(-1)
[ 350]   jmpnot     rel(-1) imm(387)
// if arg2 < arg1:
// arg1 += arg2 (from 88: 199)
[ 353]      add     rel(-3)  rel(-2)  rel(-3)
// local0 = -arg2
[ 357]      mul     rel(-2)  imm(-1)  rel(-1)
// call proc D with arg0, arg2, arg1
// third arg: arg1 + local0 = arg1+arg2-arg2 = arg1
[ 361]      add     rel(-3)  rel(-1)   rel(3)
// local0 = third arg * -1 = -arg1
[ 365]      mul      rel(3)  imm(-1)  rel(-1)
// second arg: arg1 + local0 = arg1+arg2 - arg1 = arg2
[ 369]      add     rel(-3)  rel(-1)   rel(2)
// first arg: arg0
[ 373]      add      imm(0)  rel(-4)   rel(1)
// set ret=384
[ 377]      mul      imm(1) imm(384)   rel(0)
[ 381]   jmpnot      imm(0) imm(303)
// jump to 415 (return)
[ 384]    jmpif      imm(1) imm(415)
// if arg1 <= arg2:
// arg0 *= -1 (from 27: -1) (from 88: -50)
[ 387]      mul     rel(-4)  imm(-1)  rel(-4)
// arg0 += arg1 (from 27: 0) (from 88: 0)
[ 391]      add     rel(-4)  rel(-3)  rel(-4)
// arg2 *= arg1 (from 27: Y) (from 88: x * 149 = 7450)
[ 395]      mul     rel(-3)  rel(-2)  rel(-2)
// arg0 *= arg2 (from 27: 0) (from 88: 0)
[ 399]      mul     rel(-2)  rel(-4)  rel(-4)
// arg1 *= arg2 (from 27: Y) (from 88: x * x * 149 = 149x^2)
[ 403]      mul     rel(-3)  rel(-2)  rel(-3)
// arg2 = -arg0 (from 27: 0) (from 88: 0)
[ 407]      mul     rel(-4)  imm(-1)  rel(-2)
// x0 = arg1 + arg2 (from 27: Y) (from 88: 149x^2)
[ 411]      add     rel(-3)  rel(-2)   rel(1)
// return x0 = arg1 + arg2 (from 27: Y) (from 88: 149x^2)
[ 415]      mul      imm(1)   rel(1)  rel(-4)
[ 419]   adjrel     imm(-5)
[ 421]   jmpnot      imm(0)   rel(0)