# emit_datetime.ludic — the calendar/clock half of the stdlib: the Duration.*,
# Date.* and DateTime.* namespaces (issue #9). Everything is a plain i32 integer
# epoch, never a float, so it is deterministic and bit-identical on every
# platform:
#   Duration — a span in whole seconds (Duration.hours(3) == 10800).
#   Date     — a civil day, stored as the count of days since 1970-01-01 (UTC),
#              so Date arithmetic is ordinary integer add/subtract.
#   DateTime — an instant, stored as the count of seconds since the 1970 epoch
#              (UTC), matching Time.now().
# The two civil<->epoch conversions are Howard Hinnant's public-domain algorithms
# (chrono-compatible, proleptic Gregorian), emitted once per program as the
# @lp_days_from_civil / @lp_civil_from_days prelude and gated by g_uses_datert.
# v1 is UTC-only with no leap seconds; instants are assumed non-negative (dates
# at or after 1970). Timezones, format/parse and a game-controlled simulated
# clock are tracked follow-ups.

# --- Duration.* — spans in whole seconds -------------------------------------
function is_duration_ns(meth: pointer) -> bool {
  if (meth == "seconds") or (meth == "minutes") or (meth == "hours") or (meth == "days") { return true }
  if (meth == "as_seconds") or (meth == "as_minutes") or (meth == "as_hours") or (meth == "as_days") { return true }
  return false
}

function emit_duration_ns(meth: pointer, e: Node) -> Val {
  let n = emit_expr(e.kids[0])
  if (meth == "seconds")    { return val(n.code, "int") }                       # already seconds
  if (meth == "minutes")    { return val(emit_bind(`mul i32 {n.code}, 60`), "int") }
  if (meth == "hours")      { return val(emit_bind(`mul i32 {n.code}, 3600`), "int") }
  if (meth == "days")       { return val(emit_bind(`mul i32 {n.code}, 86400`), "int") }
  if (meth == "as_seconds") { return val(n.code, "int") }
  if (meth == "as_minutes") { return val(emit_bind(`sdiv i32 {n.code}, 60`), "int") }
  if (meth == "as_hours")   { return val(emit_bind(`sdiv i32 {n.code}, 3600`), "int") }
  # as_days: whole days in the span (floor toward zero)
  return val(emit_bind(`sdiv i32 {n.code}, 86400`), "int")
}

# --- Date.* — a civil day as days-since-1970 ---------------------------------
# load one component (0=year, 1=month, 2=day) of the civil date for epoch-day
# code `ed` by calling the civil_from_days prelude into three stack slots.
function date_component(ed: pointer, which: int) -> pointer {
  g_uses_datert = true
  let yp = emit_alloca("i32")
  let mp = emit_alloca("i32")
  let dp = emit_alloca("i32")
  emit(`  call void @lp_civil_from_days(i32 {ed}, ptr {yp}, ptr {mp}, ptr {dp})\n`)
  var p = yp
  if (which == 1) { p = mp }
  if (which == 2) { p = dp }
  return emit_bind(`load i32, ptr {p}`)
}

function is_date_ns(meth: pointer) -> bool {
  if (meth == "new") or (meth == "year") or (meth == "month") or (meth == "day") { return true }
  if (meth == "weekday") or (meth == "is_leap") or (meth == "days_in_month") { return true }
  if (meth == "to_epoch") or (meth == "add_days") or (meth == "diff_days") { return true }
  return false
}

function emit_date_ns(meth: pointer, e: Node) -> Val {
  if (meth == "new") {                              # new(year, month, day) -> Date (epoch-day)
    g_uses_datert = true
    let y = emit_expr(e.kids[0]);  let m = emit_expr(e.kids[1]);  let d = emit_expr(e.kids[2])
    return val(emit_bind(`call i32 @lp_days_from_civil(i32 {y.code}, i32 {m.code}, i32 {d.code})`), "int")
  }
  if (meth == "year")  { let ed = emit_expr(e.kids[0]);  return val(date_component(ed.code, 0), "int") }
  if (meth == "month") { let ed = emit_expr(e.kids[0]);  return val(date_component(ed.code, 1), "int") }
  if (meth == "day")   { let ed = emit_expr(e.kids[0]);  return val(date_component(ed.code, 2), "int") }
  if (meth == "weekday") {                          # 0=Sunday .. 6=Saturday (1970-01-01 was Thursday)
    let ed = emit_expr(e.kids[0])
    let s = emit_bind(`add i32 {ed.code}, 4`)       # shift so the epoch's Thursday lands right
    let r = emit_bind(`srem i32 {s}, 7`)
    let rr = emit_bind(`add i32 {r}, 7`)            # normalise a negative remainder into [0,7)
    return val(emit_bind(`srem i32 {rr}, 7`), "int")
  }
  if (meth == "is_leap") {                          # proleptic Gregorian leap-year test
    let y = emit_expr(e.kids[0])
    let m4 = emit_bind(`srem i32 {y.code}, 4`);    let c4 = emit_bind(`icmp eq i32 {m4}, 0`)
    let m100 = emit_bind(`srem i32 {y.code}, 100`); let c100 = emit_bind(`icmp ne i32 {m100}, 0`)
    let m400 = emit_bind(`srem i32 {y.code}, 400`); let c400 = emit_bind(`icmp eq i32 {m400}, 0`)
    let common = emit_bind(`and i1 {c4}, {c100}`)   # divisible by 4 but not by 100
    let leap = emit_bind(`or i1 {common}, {c400}`)  # ...or divisible by 400
    return val(emit_bind(`zext i1 {leap} to i32`), "bool")
  }
  if (meth == "days_in_month") {                    # length of (year, month) = next month's day 0
    g_uses_datert = true
    let y = emit_expr(e.kids[0]);  let m = emit_expr(e.kids[1])
    let this = emit_bind(`call i32 @lp_days_from_civil(i32 {y.code}, i32 {m.code}, i32 1)`)
    let dec = emit_bind(`icmp eq i32 {m.code}, 12`)  # December rolls over to next January
    let ny = emit_bind(`add i32 {y.code}, 1`)
    let ny2 = emit_bind(`select i1 {dec}, i32 {ny}, i32 {y.code}`)
    let nm = emit_bind(`add i32 {m.code}, 1`)
    let nm2 = emit_bind(`select i1 {dec}, i32 1, i32 {nm}`)
    let next = emit_bind(`call i32 @lp_days_from_civil(i32 {ny2}, i32 {nm2}, i32 1)`)
    return val(emit_bind(`sub i32 {next}, {this}`), "int")
  }
  if (meth == "to_epoch") {                         # midnight UTC of the day, as a DateTime instant
    let ed = emit_expr(e.kids[0])
    return val(emit_bind(`mul i32 {ed.code}, 86400`), "int")
  }
  if (meth == "add_days") {                         # the day `n` days after `ed`
    let ed = emit_expr(e.kids[0]);  let n = emit_expr(e.kids[1])
    return val(emit_bind(`add i32 {ed.code}, {n.code}`), "int")
  }
  # diff_days(a, b) -> whole days from b to a (a - b)
  let a = emit_expr(e.kids[0]);  let b = emit_expr(e.kids[1])
  return val(emit_bind(`sub i32 {a.code}, {b.code}`), "int")
}

# --- DateTime.* — an instant as seconds-since-1970 ---------------------------
# seconds-of-day for instant `t`, normalised into [0, 86400) even for a negative
# instant, so hour/minute/second stay correct.
function dt_secofday(t: pointer) -> pointer {
  let r = emit_bind(`srem i32 {t}, 86400`)
  let rr = emit_bind(`add i32 {r}, 86400`)
  return emit_bind(`srem i32 {rr}, 86400`)
}

# the epoch-day (floored) an instant falls on: floor(t / 86400).
function dt_epochday(t: pointer) -> pointer {
  let sod = dt_secofday(t)                          # t - sod is an exact multiple of 86400
  let base = emit_bind(`sub i32 {t}, {sod}`)
  return emit_bind(`sdiv i32 {base}, 86400`)
}

function is_datetime_ns(meth: pointer) -> bool {
  if (meth == "from") or (meth == "date") or (meth == "add") { return true }
  if (meth == "year") or (meth == "month") or (meth == "day") or (meth == "weekday") { return true }
  if (meth == "hour") or (meth == "minute") or (meth == "second") { return true }
  if (meth == "format") or (meth == "parse") { return true }
  return false
}


# does the pattern have token `tok` (length tlen) starting at index i?
function dt_tok_at(pat: pointer, n: int, i: int, tok: pointer, tlen: int) -> bool {
  if (i + tlen) > n { return false }
  var k = 0
  while k < tlen { if pat[i + k] != tok[k] { return false };  k += 1 }
  return true
}

# DateTime.format(t, "pattern") -> string. The pattern MUST be a string literal;
# the tokens YYYY / YY / MM / DD / HH / mm / ss expand to zero-padded fields and
# every other character is copied through verbatim. Expanded at compile time into
# a fold of @lp_str_concat over literal runs and @lp_dt_pad0 field conversions.
function emit_datetime_format(e: Node) -> Val {
  g_uses_datert = true
  g_uses_str = true
  if e.kids[1].kind != E_STR { perr("DateTime.format needs a string-literal pattern") }
  let t = emit_expr(e.kids[0])
  let pat = e.kids[1].s
  let n = len(pat)
  # compute all six components once
  let ed = dt_epochday(t.code)
  let yp = emit_alloca("i32");  let mp = emit_alloca("i32");  let dp = emit_alloca("i32")
  emit(`  call void @lp_civil_from_days(i32 {ed}, ptr {yp}, ptr {mp}, ptr {dp})\n`)
  let yv = emit_bind(`load i32, ptr {yp}`)
  let mv = emit_bind(`load i32, ptr {mp}`)
  let dv = emit_bind(`load i32, ptr {dp}`)
  let sod = dt_secofday(t.code)
  let hh = emit_bind(`sdiv i32 {sod}, 3600`)
  let m3 = emit_bind(`srem i32 {sod}, 3600`)
  let mi = emit_bind(`sdiv i32 {m3}, 60`)
  let ss = emit_bind(`srem i32 {sod}, 60`)
  let yy = emit_bind(`srem i32 {yv}, 100`)
  # joined as ordinary text: each field's digits and each piece so far are freed once the next join
  # has copied them, so only the answer is left (every one of them was once kept)
  var acc = val(emit_str_const(""), "string")
  let lit = buf_new()
  var i = 0
  while i < n {
    var field: pointer = null;  var width = 0;  var tlen = 0
    if dt_tok_at(pat, n, i, "YYYY", 4) { field = yv;  width = 4;  tlen = 4 }
    else { if dt_tok_at(pat, n, i, "YY", 2) { field = yy;  width = 2;  tlen = 2 }
    else { if dt_tok_at(pat, n, i, "MM", 2) { field = mv;  width = 2;  tlen = 2 }
    else { if dt_tok_at(pat, n, i, "DD", 2) { field = dv;  width = 2;  tlen = 2 }
    else { if dt_tok_at(pat, n, i, "HH", 2) { field = hh;  width = 2;  tlen = 2 }
    else { if dt_tok_at(pat, n, i, "mm", 2) { field = mi;  width = 2;  tlen = 2 }
    else { if dt_tok_at(pat, n, i, "ss", 2) { field = ss;  width = 2;  tlen = 2 } } } } } } }
    if (field == null) { buf_putc(lit, pat[i]);  i += 1 }
    else {
      let ls = buf_str(lit)
      if len(ls) > 0 { acc = emit_str_op("+", acc, val(emit_str_const(ls), "string")) }
      let piece = fresh_val(emit_bind(`call ptr @lp_dt_pad0(i32 {field}, i32 {width})`), "string")
      acc = emit_str_op("+", acc, piece)
      lit.len = 0                                    # start a fresh literal run
      i += tlen
    }
  }
  let tail = buf_str(lit)
  if len(tail) > 0 { acc = emit_str_op("+", acc, val(emit_str_const(tail), "string")) }
  return acc
}

# DateTime.parse(s, "pattern") -> DateTime. The pattern MUST be a string literal;
# each field is read from a fixed offset (the layout the pattern fixes) and any
# non-digit where a digit is expected fails the parse, returning -1. Missing
# fields default to 1970-01-01 00:00:00.
function emit_datetime_parse(e: Node) -> Val {
  g_uses_datert = true
  if e.kids[1].kind != E_STR { perr("DateTime.parse needs a string-literal pattern") }
  let s = emit_expr(e.kids[0])
  let pat = e.kids[1].s
  let n = len(pat)
  let failp = emit_alloca("i32")
  store_at("i32", "0", failp)
  # component slots, seeded to the epoch defaults
  let yp = emit_alloca("i32");  store_at("i32", "1970", yp)
  let mp = emit_alloca("i32");  store_at("i32", "1", mp)
  let dp = emit_alloca("i32");  store_at("i32", "1", dp)
  let hp = emit_alloca("i32");  store_at("i32", "0", hp)
  let np = emit_alloca("i32");  store_at("i32", "0", np)
  let sp = emit_alloca("i32");  store_at("i32", "0", sp)
  var off = 0
  var i = 0
  while i < n {
    var slot: pointer = null;  var width = 0;  var tlen = 0
    if dt_tok_at(pat, n, i, "YYYY", 4) { slot = yp;  width = 4;  tlen = 4 }
    else { if dt_tok_at(pat, n, i, "MM", 2) { slot = mp;  width = 2;  tlen = 2 }
    else { if dt_tok_at(pat, n, i, "DD", 2) { slot = dp;  width = 2;  tlen = 2 }
    else { if dt_tok_at(pat, n, i, "HH", 2) { slot = hp;  width = 2;  tlen = 2 }
    else { if dt_tok_at(pat, n, i, "mm", 2) { slot = np;  width = 2;  tlen = 2 }
    else { if dt_tok_at(pat, n, i, "ss", 2) { slot = sp;  width = 2;  tlen = 2 } } } } } }
    if (slot == null) { off += 1;  i += 1 }
    else {
      let rd = emit_bind(`call i32 @lp_dt_rd(ptr {s.code}, i32 {itoa(off)}, i32 {width}, ptr {failp})`)
      store_at("i32", rd, slot)
      off += width
      i += tlen
    }
  }
  let y = emit_bind(`load i32, ptr {yp}`)
  let mo = emit_bind(`load i32, ptr {mp}`)
  let d = emit_bind(`load i32, ptr {dp}`)
  let h = emit_bind(`load i32, ptr {hp}`)
  let mn = emit_bind(`load i32, ptr {np}`)
  let sc = emit_bind(`load i32, ptr {sp}`)
  let ed = emit_bind(`call i32 @lp_days_from_civil(i32 {y}, i32 {mo}, i32 {d})`)
  let days = emit_bind(`mul i32 {ed}, 86400`)
  let hs = emit_bind(`mul i32 {h}, 3600`)
  let ns = emit_bind(`mul i32 {mn}, 60`)
  let a1 = emit_bind(`add i32 {days}, {hs}`)
  let a2 = emit_bind(`add i32 {a1}, {ns}`)
  let inst = emit_bind(`add i32 {a2}, {sc}`)
  let failed = emit_bind(`load i32, ptr {failp}`)
  let bad = emit_bind(`icmp ne i32 {failed}, 0`)
  return val(emit_bind(`select i1 {bad}, i32 -1, i32 {inst}`), "int")
}

function emit_datetime_ns(meth: pointer, e: Node) -> Val {
  if (meth == "format") { return emit_datetime_format(e) }
  if (meth == "parse")  { return emit_datetime_parse(e) }
  if (meth == "from") {                             # from(year, month, day, hour, minute, second) -> DateTime
    g_uses_datert = true
    let y = emit_expr(e.kids[0]);  let mo = emit_expr(e.kids[1]);  let d = emit_expr(e.kids[2])
    let h = emit_expr(e.kids[3]);  let mi = emit_expr(e.kids[4]);  let s = emit_expr(e.kids[5])
    let ed = emit_bind(`call i32 @lp_days_from_civil(i32 {y.code}, i32 {mo.code}, i32 {d.code})`)
    let days = emit_bind(`mul i32 {ed}, 86400`)
    let hh = emit_bind(`mul i32 {h.code}, 3600`)
    let mm = emit_bind(`mul i32 {mi.code}, 60`)
    let a = emit_bind(`add i32 {days}, {hh}`)
    let b = emit_bind(`add i32 {a}, {mm}`)
    return val(emit_bind(`add i32 {b}, {s.code}`), "int")
  }
  if (meth == "date") {                             # the calendar day this instant is on -> Date
    let t = emit_expr(e.kids[0])
    return val(dt_epochday(t.code), "int")
  }
  if (meth == "add") {                              # the instant `dur` seconds after `t`
    let t = emit_expr(e.kids[0]);  let dur = emit_expr(e.kids[1])
    return val(emit_bind(`add i32 {t.code}, {dur.code}`), "int")
  }
  if (meth == "year")  { let t = emit_expr(e.kids[0]);  return val(date_component(dt_epochday(t.code), 0), "int") }
  if (meth == "month") { let t = emit_expr(e.kids[0]);  return val(date_component(dt_epochday(t.code), 1), "int") }
  if (meth == "day")   { let t = emit_expr(e.kids[0]);  return val(date_component(dt_epochday(t.code), 2), "int") }
  if (meth == "weekday") {                          # 0=Sunday .. 6=Saturday
    let t = emit_expr(e.kids[0])
    let ed = dt_epochday(t.code)
    let s = emit_bind(`add i32 {ed}, 4`)
    let r = emit_bind(`srem i32 {s}, 7`)
    let rr = emit_bind(`add i32 {r}, 7`)
    return val(emit_bind(`srem i32 {rr}, 7`), "int")
  }
  if (meth == "hour") {                             # 0..23
    let t = emit_expr(e.kids[0])
    let sod = dt_secofday(t.code)
    return val(emit_bind(`sdiv i32 {sod}, 3600`), "int")
  }
  if (meth == "minute") {                           # 0..59
    let t = emit_expr(e.kids[0])
    let sod = dt_secofday(t.code)
    let h = emit_bind(`srem i32 {sod}, 3600`)
    return val(emit_bind(`sdiv i32 {h}, 60`), "int")
  }
  # second: 0..59
  let t = emit_expr(e.kids[0])
  let sod = dt_secofday(t.code)
  return val(emit_bind(`srem i32 {sod}, 60`), "int")
}

# emit_datetime_prelude — the two civil<->epoch conversions, emitted once per
# program that uses Date/DateTime (g_uses_datert). Both are Howard Hinnant's
# public-domain proleptic-Gregorian algorithms, in pure i32 integer IR, so they
# are deterministic and bit-identical everywhere. 719468 is the day count from
# 0000-03-01 to 1970-01-01; 146097 is the days in a 400-year era.
function emit_datetime_prelude() -> void {
  # @lp_days_from_civil(y, m, d) -> days since 1970-01-01
  emith("define i32 @lp_days_from_civil(i32 %y0, i32 %m, i32 %d) {\n")
  emith("  %mle2 = icmp sle i32 %m, 2\n")
  emith("  %ysub = select i1 %mle2, i32 1, i32 0\n")
  emith("  %y = sub i32 %y0, %ysub\n")
  emith("  %yneg = icmp slt i32 %y, 0\n")
  emith("  %ym399 = sub i32 %y, 399\n")
  emith("  %enum = select i1 %yneg, i32 %ym399, i32 %y\n")
  emith("  %era = sdiv i32 %enum, 400\n")
  emith("  %era400 = mul i32 %era, 400\n")
  emith("  %yoe = sub i32 %y, %era400\n")
  emith("  %mgt2 = icmp sgt i32 %m, 2\n")
  emith("  %mshift = select i1 %mgt2, i32 -3, i32 9\n")
  emith("  %mm = add i32 %m, %mshift\n")
  emith("  %t153 = mul i32 153, %mm\n")
  emith("  %t153b = add i32 %t153, 2\n")
  emith("  %doy0 = sdiv i32 %t153b, 5\n")
  emith("  %doy1 = add i32 %doy0, %d\n")
  emith("  %doy = sub i32 %doy1, 1\n")
  emith("  %yoe365 = mul i32 %yoe, 365\n")
  emith("  %yoe4 = sdiv i32 %yoe, 4\n")
  emith("  %yoe100 = sdiv i32 %yoe, 100\n")
  emith("  %doe0 = add i32 %yoe365, %yoe4\n")
  emith("  %doe1 = sub i32 %doe0, %yoe100\n")
  emith("  %doe = add i32 %doe1, %doy\n")
  emith("  %e146097 = mul i32 %era, 146097\n")
  emith("  %r0 = add i32 %e146097, %doe\n")
  emith("  %r = sub i32 %r0, 719468\n")
  emith("  ret i32 %r\n")
  emith("}\n")
  # @lp_civil_from_days(z0, yp, mp, dp): write the civil (year, month, day) of
  # the epoch-day z0 through the three out-pointers.
  emith("define void @lp_civil_from_days(i32 %z0, ptr %yp, ptr %mp, ptr %dp) {\n")
  emith("  %z = add i32 %z0, 719468\n")
  emith("  %zneg = icmp slt i32 %z, 0\n")
  emith("  %zm = sub i32 %z, 146096\n")
  emith("  %enum = select i1 %zneg, i32 %zm, i32 %z\n")
  emith("  %era = sdiv i32 %enum, 146097\n")
  emith("  %era146097 = mul i32 %era, 146097\n")
  emith("  %doe = sub i32 %z, %era146097\n")
  emith("  %d1460 = sdiv i32 %doe, 1460\n")
  emith("  %d36524 = sdiv i32 %doe, 36524\n")
  emith("  %d146096 = sdiv i32 %doe, 146096\n")
  emith("  %ya = sub i32 %doe, %d1460\n")
  emith("  %yb = add i32 %ya, %d36524\n")
  emith("  %yc = sub i32 %yb, %d146096\n")
  emith("  %yoe = sdiv i32 %yc, 365\n")
  emith("  %era400 = mul i32 %era, 400\n")
  emith("  %yy = add i32 %yoe, %era400\n")
  emith("  %yoe365 = mul i32 %yoe, 365\n")
  emith("  %yoe4 = sdiv i32 %yoe, 4\n")
  emith("  %yoe100 = sdiv i32 %yoe, 100\n")
  emith("  %sub0 = add i32 %yoe365, %yoe4\n")
  emith("  %sub1 = sub i32 %sub0, %yoe100\n")
  emith("  %doy = sub i32 %doe, %sub1\n")
  emith("  %fivedoy = mul i32 5, %doy\n")
  emith("  %fivedoy2 = add i32 %fivedoy, 2\n")
  emith("  %mpv = sdiv i32 %fivedoy2, 153\n")
  emith("  %m153 = mul i32 153, %mpv\n")
  emith("  %m153b = add i32 %m153, 2\n")
  emith("  %m153c = sdiv i32 %m153b, 5\n")
  emith("  %dd0 = sub i32 %doy, %m153c\n")
  emith("  %dd = add i32 %dd0, 1\n")
  emith("  %mplt10 = icmp slt i32 %mpv, 10\n")
  emith("  %mplus3 = add i32 %mpv, 3\n")
  emith("  %mminus9 = sub i32 %mpv, 9\n")
  emith("  %mfin = select i1 %mplt10, i32 %mplus3, i32 %mminus9\n")
  emith("  %mmle2 = icmp sle i32 %mfin, 2\n")
  emith("  %yinc = select i1 %mmle2, i32 1, i32 0\n")
  emith("  %yfin = add i32 %yy, %yinc\n")
  emith("  store i32 %yfin, ptr %yp\n")
  emith("  store i32 %mfin, ptr %mp\n")
  emith("  store i32 %dd, ptr %dp\n")
  emith("  ret void\n")
  emith("}\n")
  # @lp_dt_pad0(v, w): a fresh, malloc'd, w-digit zero-padded decimal of v
  # (v assumed non-negative). Backs DateTime.format's numeric fields.
  emith("define ptr @lp_dt_pad0(i32 %v, i32 %w) {\n")
  emith("  %we = zext i32 %w to i64\n")
  emith("  %sz = add i64 %we, 1\n")
  emith("  %buf = call ptr @lp_malloc(i64 %sz)\n")
  emith("  %endp = getelementptr i8, ptr %buf, i32 %w\n")
  emith("  store i8 0, ptr %endp\n")
  emith("  %kp = alloca i32\n  %vp = alloca i32\n")
  emith("  %km1 = sub i32 %w, 1\n  store i32 %km1, ptr %kp\n  store i32 %v, ptr %vp\n")
  emith("  br label %loop\n")
  emith("loop:\n  %k = load i32, ptr %kp\n  %kok = icmp sge i32 %k, 0\n  br i1 %kok, label %body, label %done\n")
  emith("body:\n  %vv = load i32, ptr %vp\n  %d = srem i32 %vv, 10\n  %ch = add i32 %d, 48\n  %ch8 = trunc i32 %ch to i8\n")
  emith("  %cp = getelementptr i8, ptr %buf, i32 %k\n  store i8 %ch8, ptr %cp\n")
  emith("  %vn = sdiv i32 %vv, 10\n  store i32 %vn, ptr %vp\n  %kn = sub i32 %k, 1\n  store i32 %kn, ptr %kp\n  br label %loop\n")
  emith("done:\n  ret ptr %buf\n}\n")
  # @lp_dt_rd(s, off, w, failp): read w decimal digits of s starting at off into an
  # int; on any non-digit set *failp = 1. Backs DateTime.parse's fixed-width fields.
  emith("define i32 @lp_dt_rd(ptr %s, i32 %off, i32 %w, ptr %failp) {\n")
  emith("  %accp = alloca i32\n  store i32 0, ptr %accp\n  %kp = alloca i32\n  store i32 0, ptr %kp\n")
  emith("  br label %loop\n")
  emith("loop:\n  %k = load i32, ptr %kp\n  %kok = icmp slt i32 %k, %w\n  br i1 %kok, label %body, label %done\n")
  emith("body:\n  %idx = add i32 %off, %k\n  %cp = getelementptr i8, ptr %s, i32 %idx\n  %c8 = load i8, ptr %cp\n  %c = sext i8 %c8 to i32\n")
  emith("  %zero = icmp eq i32 %c, 0\n  br i1 %zero, label %stop, label %digit\n")   # stop at the terminator, never read past it
  emith("stop:\n  store i32 1, ptr %failp\n  br label %done\n")
  emith("digit:\n  %lt = icmp slt i32 %c, 48\n  %gt = icmp sgt i32 %c, 57\n  %isbad = or i1 %lt, %gt\n  br i1 %isbad, label %fail, label %ok\n")
  emith("fail:\n  store i32 1, ptr %failp\n  br label %next\n")
  emith("ok:\n  %acc0 = load i32, ptr %accp\n  %m10 = mul i32 %acc0, 10\n  %dg = sub i32 %c, 48\n  %acc1 = add i32 %m10, %dg\n  store i32 %acc1, ptr %accp\n  br label %next\n")
  emith("next:\n  %kn = add i32 %k, 1\n  store i32 %kn, ptr %kp\n  br label %loop\n")
  emith("done:\n  %r = load i32, ptr %accp\n  ret i32 %r\n}\n")
}

# --- Clock.* — a game-controlled simulated clock -----------------------------
# @L_clock (declared in emit_head, universal) is a plain seconds counter the game
# owns: unlike Time.now / Time.since, it never touches the wall clock, so gameplay
# that reads Clock.now() is deterministic and replay-safe. Advance it however the
# simulation dictates (e.g. by Duration.* each tick), or set it outright.
function is_clock_ns(meth: pointer) -> bool {
  if (meth == "now") or (meth == "set") or (meth == "advance") or (meth == "reset") { return true }
  return false
}

function emit_clock_ns(meth: pointer, e: Node) -> Val {
  if (meth == "now") {                              # the current simulated instant
    return val(emit_bind("load i32, ptr @L_clock"), "int")
  }
  if (meth == "reset") {                            # back to the epoch (0)
    emit("  store i32 0, ptr @L_clock\n")
    return val("0", "void")
  }
  if (meth == "set") {                              # set the clock to instant t
    let t = emit_expr(e.kids[0])
    emit(`  store i32 {t.code}, ptr @L_clock\n`)
    return val("0", "void")
  }
  # advance: move the clock forward by a Duration (seconds)
  let d = emit_expr(e.kids[0])
  let cur = emit_bind("load i32, ptr @L_clock")
  let nv = emit_bind(`add i32 {cur}, {d.code}`)
  emit(`  store i32 {nv}, ptr @L_clock\n`)
  return val("0", "void")
}