From af191dbfa9f5b8f729ed484cfde7aa6ab5d4f3cf Mon Sep 17 00:00:00 2001
From: flywind <43030857+xflywind@users.noreply.github.com>
Date: Thu, 7 Jan 2021 01:48:02 -0600
Subject: [PATCH] add math.signbit (#16592)

---
 changelog.md           |  3 +++
 compiler/vmops.nim     |  6 ++++++
 lib/pure/math.nim      | 27 ++++++++++++++++++++++++++-
 tests/stdlib/tmath.nim | 10 ++++++++++
 4 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/changelog.md b/changelog.md
index 306cf54d31e39..4e9b8c1622f59 100644
--- a/changelog.md
+++ b/changelog.md
@@ -93,6 +93,9 @@
 with other backends. see #9125. Use `-d:nimLegacyJsRound` for previous behavior.
 
 
+
+- Added `math.signbit`.
+
 ## Language changes
 
 - `nimscript` now handles `except Exception as e`.
diff --git a/compiler/vmops.nim b/compiler/vmops.nim
index 3e859d3d7f646..504a352b507ac 100644
--- a/compiler/vmops.nim
+++ b/compiler/vmops.nim
@@ -16,6 +16,9 @@ from math import sqrt, ln, log10, log2, exp, round, arccos, arcsin,
 when declared(math.copySign):
   from math import copySign
 
+when declared(math.signbit):
+  from math import signbit
+
 from os import getEnv, existsEnv, dirExists, fileExists, putEnv, walkDir, getAppFilename
 from md5 import getMD5
 from sighashes import symBodyDigest
@@ -174,6 +177,9 @@ proc registerAdditionalOps*(c: PCtx) =
   when declared(copySign):
     wrap2f_math(copySign)
 
+  when declared(signbit):
+    wrap1f_math(signbit)
+
   wrap1s(getMD5, md5op)
 
   proc `mod Wrapper`(a: VmArgs) {.nimcall.} =
diff --git a/lib/pure/math.nim b/lib/pure/math.nim
index a6a3676b99c7d..bcda68afe1ea5 100644
--- a/lib/pure/math.nim
+++ b/lib/pure/math.nim
@@ -56,7 +56,7 @@ import std/private/since
 {.push debugger: off.} # the user does not want to trace a part
                        # of the standard library!
 
-import bitops, fenv
+import std/[bitops, fenv]
 
 when defined(c) or defined(cpp):
   proc c_isnan(x: float): bool {.importc: "isnan", header: "<math.h>".}
@@ -65,6 +65,8 @@ when defined(c) or defined(cpp):
   proc c_copysign(x, y: cfloat): cfloat {.importc: "copysignf", header: "<math.h>".}
   proc c_copysign(x, y: cdouble): cdouble {.importc: "copysign", header: "<math.h>".}
 
+  proc c_signbit(x: SomeFloat): cint {.importc: "signbit", header: "<math.h>".}
+
 func binom*(n, k: int): int =
   ## Computes the `binomial coefficient <https://en.wikipedia.org/wiki/Binomial_coefficient>`_.
   runnableExamples:
@@ -156,6 +158,29 @@ func isNaN*(x: SomeFloat): bool {.inline, since: (1,5,1).} =
     when defined(js): fn()
     else: result = c_isnan(x)
 
+when defined(js):
+  proc toBitsImpl(x: float): array[2, uint32] =
+    asm """
+    const buffer = new ArrayBuffer(8);
+    const floatBuffer = new Float64Array(buffer);
+    const uintBuffer = new Uint32Array(buffer);
+    floatBuffer[0] = `x`;
+    `result` = uintBuffer
+    """
+
+proc signbit*(x: SomeFloat): bool {.inline, since: (1, 5, 1).} =
+  ## Returns true if `x` is negative, false otherwise.
+  runnableExamples:
+    doAssert not signbit(0.0)
+    doAssert signbit(-0.0)
+    doAssert signbit(-0.1)
+    doAssert not signbit(0.1)
+  when defined(js):
+    let uintBuffer = toBitsImpl(x)
+    result = (uintBuffer[1] shr 31) != 0
+  else:
+    result = c_signbit(x) != 0
+
 func copySign*[T: SomeFloat](x, y: T): T {.inline, since: (1, 5, 1).} =
   ## Returns a value with the magnitude of `x` and the sign of `y`;
   ## this works even if x or y are NaN or zero, both of which can carry a sign.
diff --git a/tests/stdlib/tmath.nim b/tests/stdlib/tmath.nim
index e5cb58ebab8bd..62fdcd19f64c9 100644
--- a/tests/stdlib/tmath.nim
+++ b/tests/stdlib/tmath.nim
@@ -304,6 +304,16 @@ block:
 
 template main =
   # xxx wrap all under `main` so it also gets tested in vm.
+  block: # signbit
+    doAssert not signbit(0.0)
+    doAssert signbit(-0.0)
+    doAssert signbit(-0.1)
+    doAssert not signbit(0.1)
+
+    doAssert not signbit(Inf)
+    doAssert signbit(-Inf)
+    doAssert not signbit(NaN)
+
   block: # isNaN
     doAssert NaN.isNaN
     doAssert not Inf.isNaN