printing float values will have one more digit. (nim-lang#13276) [backport]

* printing float values will have one more digit. Fixes nim-lang#13196

Author: krux02

lib/pure/json.nim

@@ -677,7 +677,7 @@ proc pretty*(node: JsonNode, indent = 2): string =
   ## Similar to prettyprint in Python.
   runnableExamples:
     let j = %* {"name": "Isaac", "books": ["Robot Dreams"],
-                "details": {"age": 35, "pi": 3.1415}}
+                "details": {"age": 35, "number": 3.125}}
     doAssert pretty(j) == """
 {
   "name": "Isaac",
@@ -686,7 +686,7 @@ proc pretty*(node: JsonNode, indent = 2): string =
   ],
   "details": {
     "age": 35,
-    "pi": 3.1415
+    "number": 3.125
   }
 }"""
   result = ""

lib/system/formatfloat.nim

@@ -29,7 +29,7 @@ proc writeFloatToBuffer*(buf: var array[65, char]; value: BiggestFloat): int =
   ## * `buf` - A buffer to write into. The buffer does not need to be
   ##           initialized and it will be overridden.
   ##
-  var n: int = c_sprintf(addr buf, "%.16g", value)
+  var n: int = c_sprintf(addr buf, "%.17g", value)
   var hasDot = false
   for i in 0..n-1:
     if buf[i] == ',':

tests/errmsgs/tsigmatch.nim

@@ -58,7 +58,7 @@ proc f(a1: string; a2: varargs[string]; a3: float; a4: var string)
   required type for a4: var string
   but expression '"bad"' is immutable, not 'var'
 
-expression: f("asdf", "1", "2", "3", "4", 2.3, "bad")
+expression: f("asdf", "1", "2", "3", "4", 2.25, "bad")
 tsigmatch.nim(164, 4) Error: type mismatch: got <string, a0: int literal(12)>
 but expected one of:
 proc f(x: string; a0: var int)
@@ -153,7 +153,7 @@ block:
   # sigmatch gets confused with param/arg position after varargs
   proc f(a1: int) = discard
   proc f(a1: string, a2: varargs[string], a3: float, a4: var string) = discard
-  f("asdf", "1", "2", "3", "4", 2.3, "bad")
+  f("asdf", "1", "2", "3", "4", 2.25, "bad")
 
 block:
   # bug: https://github.com/nim-lang/Nim/issues/11061#issuecomment-508970046
@@ -169,4 +169,3 @@ block:
   proc fun1(a1: MyInt, a2: Mystring) = discard
   proc fun1(a1: float, a2: Mystring) = discard
   fun1(Mystring.default, "asdf")
-

tests/float/tfloat6.nim

@@ -1,23 +1,14 @@
 discard """
-  output: '''
-1e-06 : 1e-06
-1e-06 : 1e-06
-0.001 : 0.001
-1e-06 : 1e-06
-1e-06 : 1e-06
-10.000001 : 10.000001
-100.000001 : 100.000001
-'''
-  disabled: "windows"
+disabled: "windows"
 """
 
 import strutils
 
-echo "0.00_0001".parseFloat(), " : ", 1E-6
-echo "0.00__00_01".parseFloat(), " : ", 1E-6
-echo "0.0_01".parseFloat(), " : ", 0.001
-echo "0.00_000_1".parseFloat(), " : ", 1E-6
-echo "0.00000_1".parseFloat(), " : ", 1E-6
+doAssert "0.00_0001".parseFloat() == 1E-6
+doAssert "0.00__00_01".parseFloat() == 1E-6
+doAssert "0.0_01".parseFloat() == 0.001
+doAssert "0.00_000_1".parseFloat() == 1E-6
+doAssert "0.00000_1".parseFloat() == 1E-6
 
-echo "1_0.00_0001".parseFloat(), " : ", 10.000001
-echo "1__00.00_0001".parseFloat(), " : ", 1_00.000001
+doAssert "1_0.00_0001".parseFloat() == 10.000001
+doAssert "1__00.00_0001".parseFloat() == 1_00.000001

tests/float/tfloat8.nim

@@ -0,0 +1,19 @@
+discard """
+disabled: windows
+"""
+
+{.passL: "-lm".} # not sure how to do this on windows
+
+import strutils
+
+proc nextafter(a,b: float64): float64 {.importc: "nextafter", header: "<math.h>".}
+
+var myFloat = 2.5
+
+for i in 0 .. 100:
+  let newFloat = nextafter(myFloat, Inf)
+  let oldStr = $myFloat
+  let newStr = $newFloat
+  doAssert parseFloat(newStr) == newFloat
+  doAssert oldStr != newStr
+  myFloat = newFloat

tests/generics/tforwardgeneric.nim

@@ -1,11 +1,11 @@
 discard """
-  output: "1.1 11\n42\n0"
+  output: "1.125 11\n42\n0"
   ccodecheck: "!@'ClEnv'"
 """
 
 proc p[T](a, b: T): T
 
-echo p(0.9, 0.1), " ", p(9, 1)
+echo p(0.875, 0.125), " ", p(9, 1)
 
 proc p[T](a, b: T): T =
   let c = b
@@ -25,4 +25,3 @@ proc print[T](t: T) =
   echo t
 
 echo bar()
-

tests/generics/tgenerics_issues.nim

@@ -6,7 +6,7 @@ discard """
 perm: 22 det: 22
 TMatrix[3, 3, system.int]
 3
-@[0.9, 0.1]
+@[0.875, 0.125]
 U[3]
 U[(f: 3)]
 U[[3]]
@@ -20,9 +20,9 @@ concrete 88
 2
 3
 !!Hi!!
-G:0,1:0.1
-G:0,1:0.1
-H:1:0.1
+G:0,1:0.125
+G:0,1:0.125
+H:1:0.125
 '''
 joinable: false
 """
@@ -370,7 +370,7 @@ block t2304:
   type TV2[T:SomeNumber] = array[0..1, T]
   proc newV2T[T](x, y: T=0): TV2[T] = [x, y]
 
-  let x = newV2T[float](0.9, 0.1)
+  let x = newV2T[float](0.875, 0.125)
   echo(@x)
 
 
@@ -711,7 +711,7 @@ block t4863:
   proc q[j: static[int]](x:H[j]) = echo "H:", j, ":", x.v
 
   var
-    g0 = G[0,1](v: 0.1)
+    g0 = G[0,1](v: 0.125)
     h0:H[1] = g0
   p(g0)
   p(h0)

tests/objects/t12753.nim

@@ -1,7 +1,7 @@
 discard """
   output: '''
-(v: [(v: [0.0, 1.1]), (v: [2.2, 3.3])])
-(v: [(v: [0.0, 1.1]), (v: [2.2, 3.3])])
+(v: [(v: [0.0, 1.125]), (v: [2.25, 3.375])])
+(v: [(v: [0.0, 1.125]), (v: [2.25, 3.375])])
 '''
 """
 
@@ -13,7 +13,7 @@ type
 
 var
   a = M(v:[ V(v:[0.0,1.0]), V(v:[2.0,3.0]) ])
-  b = M(v:[ V(v:[0.0,0.1]), V(v:[0.2,0.3]) ])
+  b = M(v:[ V(v:[0.0,0.125]), V(v:[0.25,0.375]) ])
 
 echo M(v: [V(v: [b.v[0].v[0] + a.v[0].v[0], b.v[0].v[1] + a.v[0].v[1]]),
        V(v: [b.v[1].v[0] + a.v[1].v[0], b.v[1].v[1] + a.v[1].v[1]])])

tests/showoff/tdrdobbs_examples.nim

@@ -1,7 +1,7 @@
 discard """
   output: '''108
 11 -1 1936
-0.4
+0.5
 true
 truefalse'''
 """
@@ -75,7 +75,7 @@ proc evaluate(n: Formula, varToVal: proc (name: string): float): float =
   of fkMul: evaluate(n.left, varToVal) * evaluate(n.right, varToVal)
   of fkExp: pow(evaluate(n.left, varToVal), evaluate(n.right, varToVal))
 
-echo evaluate(Formula(kind: fkLit, value: 0.4), nil)
+echo evaluate(Formula(kind: fkLit, value: 0.5), nil)
 
 proc isPolyTerm(n: Formula): bool =
   n.kind == fkMul and n.left.kind == fkLit and (let e = n.right;

tests/system/tostring.nim

@@ -11,10 +11,6 @@ doAssert """["", "foo", "bar"]""" == $(@["", "foo", "bar"].toOpenArray(0, 2))
 # bug #2395
 let alphaSet: set[char] = {'a'..'c'}
 doAssert "{'a', 'b', 'c'}" == $alphaSet
-doAssert "2.3242" == $(2.3242)
-doAssert "2.982" == $(2.982)
-doAssert "123912.1" == $(123912.1)
-doAssert "123912.1823" == $(123912.1823)
 doAssert "5.0" == $(5.0)
 doAssert "1e+100" == $(1e100)
 doAssert "inf" == $(1e1000000)