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discard """
file: "tvarnums.nim"
output: "Success!"
"""
# Test variable length binary integers
import
strutils
type
TBuffer = array[0..10, int8]
proc toVarNum(x: int32, b: var TBuffer) =
# encoding: first bit indicates end of number (0 if at end)
# second bit of the first byte denotes the sign (1 --> negative)
var a = x
if x != low(x):
# low(int) is a special case,
# because abs() does not work here!
# we leave x as it is and use the check >% instead of >
# for low(int) this is needed and positive numbers are not affected
# anyway
a = abs(x)
# first 6 bits:
b[0] = toU8(ord(a >% 63'i32) shl 7 or (ord(x < 0'i32) shl 6) or (int(a) and 63))
a = a shr 6'i32 # skip first 6 bits
var i = 1
while a != 0'i32:
b[i] = toU8(ord(a >% 127'i32) shl 7 or (int(a) and 127))
inc(i)
a = a shr 7'i32
proc toVarNum64(x: int64, b: var TBuffer) =
# encoding: first bit indicates end of number (0 if at end)
# second bit of the first byte denotes the sign (1 --> negative)
var a = x
if x != low(x):
# low(int) is a special case,
# because abs() does not work here!
# we leave x as it is and use the check >% instead of >
# for low(int) this is needed and positive numbers are not affected
# anyway
a = abs(x)
# first 6 bits:
b[0] = toU8(ord(a >% 63'i64) shl 7 or (ord(x < 0'i64) shl 6) or int(a and 63))
a = a shr 6 # skip first 6 bits
var i = 1
while a != 0'i64:
b[i] = toU8(ord(a >% 127'i64) shl 7 or int(a and 127))
inc(i)
a = a shr 7
proc toNum64(b: TBuffer): int64 =
# treat first byte different:
result = ze64(b[0]) and 63
var
i = 0
Shift = 6'i64
while (ze(b[i]) and 128) != 0:
inc(i)
result = result or ((ze64(b[i]) and 127) shl Shift)
inc(Shift, 7)
if (ze(b[0]) and 64) != 0: # sign bit set?
result = not result +% 1
# this is the same as ``- result``
# but gives no overflow error for low(int)
proc toNum(b: TBuffer): int32 =
# treat first byte different:
result = int32 ze(b[0]) and 63
var
i = 0
Shift = 6'i32
while (ze(b[i]) and 128) != 0:
inc(i)
result = result or ((int32(ze(b[i])) and 127'i32) shl Shift)
Shift = Shift + 7'i32
if (ze(b[0]) and (1 shl 6)) != 0: # sign bit set?
result = (not result) +% 1'i32
# this is the same as ``- result``
# but gives no overflow error for low(int)
proc toBinary(x: int64): string =
result = newString(64)
for i in 0..63:
result[63-i] = chr((int(x shr i) and 1) + ord('0'))
proc t64(i: int64) =
var
b: TBuffer
toVarNum64(i, b)
var x = toNum64(b)
if x != i:
writeLine(stdout, $i)
writeLine(stdout, toBinary(i))
writeLine(stdout, toBinary(x))
proc t32(i: int32) =
var
b: TBuffer
toVarNum(i, b)
var x = toNum(b)
if x != i:
writeLine(stdout, toBinary(i))
writeLine(stdout, toBinary(x))
proc tm(i: int32) =
var
b: TBuffer
toVarNum64(i, b)
var x = toNum(b)
if x != i:
writeLine(stdout, toBinary(i))
writeLine(stdout, toBinary(x))
t32(0)
t32(1)
t32(-1)
t32(-100_000)
t32(100_000)
t32(low(int32))
t32(high(int32))
t64(low(int64))
t64(high(int64))
t64(0)
t64(-1)
t64(1)
t64(1000_000)
t64(-1000_000)
tm(0)
tm(1)
tm(-1)
tm(-100_000)
tm(100_000)
tm(low(int32))
tm(high(int32))
writeLine(stdout, "Success!") #OUT Success!
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