diff --git a/src/DecFP.jl b/src/DecFP.jl
index f542a6b..db35246 100644
--- a/src/DecFP.jl
+++ b/src/DecFP.jl
@@ -566,6 +566,43 @@ function Base.decompose(x::DecimalFloatingPoint)::Tuple{BigInt, Int, BigInt}
     end
 end
 
+"""
+    Dec32(x::Union{Real, AbstractString} [, mode::RoundingMode])
+    Dec32([sign::Integer,] significand::Integer, exponent::Integer)
+"""
+function Dec32(sign::Integer, significand::Integer, exponent::Integer)
+    -1 <= sign <= 1 || throw(DomainError(sign, "sign must be -1, 0, or +1"))
+    significand == 0 && return flipsign(zero(Dec32), sign)
+    sign == 0 && throw(DomainError(sign, "sign must be -1 or +1 for non-zero significand"))
+    sb = signbit(sign) ? 0x80000000 : zero(UInt32)
+    e = exponent + 101
+    s = Int32(abs(significand))
+    while s >= 10000000 # Int(maxintfloat(Dec32))
+        q, r = divrem(s, Int32(10))
+        r != 0 && throw(InexactError(:Dec32, Dec32, (sign, significand, exponent)))
+        s = q
+        e += 1
+    end
+    while e > 191 && s < 1000000 # Int(maxintfloat(Dec32) / 10)
+        s *= Int32(10)
+        e -= 1
+    end
+    e > 191 && throw(InexactError(:Dec32, Dec32, (sign, significand, exponent)))
+    while e < 0
+        q, r = divrem(s, Int32(10))
+        r != 0 && throw(InexactError(:Dec32, Dec32, (sign, significand, exponent)))
+        s = q
+        e += 1
+    end
+    # check whether significand will fit in 23 bits
+    if s < 0x00200000
+        return reinterpret(Dec32, sb | (UInt32(e) << 23) | s)
+    end
+    return reinterpret(Dec32, sb | 0x60000000 | (UInt32(e) << 21) | (s & 0x001fffff))
+end
+
+Dec32(significand::Integer, exponent::Integer) = Dec32(sign(significand), significand, exponent)
+
 function sigexp(x::Dec32)
     n = reinterpret(UInt32, x)
     if n & 0x60000000 == 0x60000000
@@ -579,6 +616,43 @@ function sigexp(x::Dec32)
     return s, e
 end
 
+"""
+    Dec64(x::Union{Real, AbstractString} [, mode::RoundingMode])
+    Dec64([sign::Integer,] significand::Integer, exponent::Integer)
+"""
+function Dec64(sign::Integer, significand::Integer, exponent::Integer)
+    -1 <= sign <= 1 || throw(DomainError(sign, "sign must be -1, 0, or +1"))
+    significand == 0 && return flipsign(zero(Dec64), sign)
+    sign == 0 && throw(DomainError(sign, "sign must be -1 or +1 for non-zero significand"))
+    sb = signbit(sign) ? 0x8000000000000000 : zero(UInt64)
+    e = exponent + 398
+    s = Int64(abs(significand))
+    while s >= 10000000000000000 # Int64(maxintfloat(Dec64))
+        q, r = divrem(s, 10)
+        r != 0 && throw(InexactError(:Dec64, Dec64, (sign, significand, exponent)))
+        s = q
+        e += 1
+    end
+    while e > 767 && s < 1000000000000000 # Int64(maxintfloat(Dec64) / 10)
+        s *= 10
+        e -= 1
+    end
+    e > 767 && throw(InexactError(:Dec64, Dec64, (sign, significand, exponent)))
+    while e < 0
+        q, r = divrem(s, 10)
+        r != 0 && throw(InexactError(:Dec64, Dec64, (sign, significand, exponent)))
+        s = q
+        e += 1
+    end
+    # check whether significand will fit in 53 bits
+    if s < 0x0020000000000000
+        return reinterpret(Dec64, sb | (UInt64(e) << 53) | s)
+    end
+    return reinterpret(Dec64, sb | 0x6000000000000000 | (UInt64(e) << 51) | (s & 0x0007ffffffffffff))
+end
+
+Dec64(significand::Integer, exponent::Integer) = Dec64(sign(significand), significand, exponent)
+
 function sigexp(x::Dec64)
     n = reinterpret(UInt64, x)
     if n & 0x6000000000000000 == 0x6000000000000000
@@ -592,6 +666,43 @@ function sigexp(x::Dec64)
     return s, e
 end
 
+"""
+    Dec128(x::Union{Real, AbstractString} [, mode::RoundingMode])
+    Dec128([sign::Integer,] significand::Integer, exponent::Integer)
+"""
+function Dec128(sign::Integer, significand::Integer, exponent::Integer)
+    -1 <= sign <= 1 || throw(DomainError(sign, "sign must be -1, 0, or +1"))
+    significand == 0 && return flipsign(zero(Dec128), sign)
+    sign == 0 && throw(DomainError(sign, "sign must be -1 or +1 for non-zero significand"))
+    sb = signbit(sign) ? 0x80000000000000000000000000000000 : zero(UInt128)
+    e = exponent + 6176
+    s = Int128(abs(significand))
+    while s >= 10000000000000000000000000000000000 # Int128(maxintfloat(Dec128))
+        q, r = divrem(s, 10)
+        r != 0 && throw(InexactError(:Dec128, Dec128, (sign, significand, exponent)))
+        s = q
+        e += 1
+    end
+    while e > 12287 && s < 1000000000000000000000000000000000 # Int128(maxintfloat(Dec128) / 10)
+        s *= 10
+        e -= 1
+    end
+    e > 12287 && throw(InexactError(:Dec128, Dec128, (sign, significand, exponent)))
+    while e < 0
+        q, r = divrem(s, 10)
+        r != 0 && throw(InexactError(:Dec128, Dec128, (sign, significand, exponent)))
+        s = q
+        e += 1
+    end
+    # check whether significand will fit in 113 bits
+    if s < 0x00020000000000000000000000000000
+        return reinterpret(Dec128, sb | (UInt128(e) << 113) | s)
+    end
+    return reinterpret(Dec128, sb | 0x60000000000000000000000000000000 | (UInt128(e) << 111) | (s & 0x00007fffffffffffffffffffffffffff))
+end
+
+Dec128(significand::Integer, exponent::Integer) = Dec128(sign(significand), significand, exponent)
+
 function sigexp(x::Dec128)
     n = reinterpret(UInt128, x)
     if n & 0x60000000000000000000000000000000 == 0x60000000000000000000000000000000
diff --git a/test/runtests.jl b/test/runtests.jl
index b3fab5b..a9fb71b 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -26,18 +26,48 @@ for T in (Dec32, Dec64, Dec128)
 
     if T == Dec32
         @test d32"3.2" * d32"4.5" == d32"14.4"
+        @test T(1, Int32(maxintfloat(T)), 0) == maxintfloat(T)
+        @test T(1, Int32(maxintfloat(T) * 100), -2) == maxintfloat(T)
+        @test T(1, Int32(maxintfloat(T) - 1), 90) == floatmax(T)
+        @test_throws InexactError T(1, Int32(maxintfloat(T)), 90)
+        @test_throws InexactError T(1, Int32(maxintfloat(T)) + 1, 0)
+        @test T(1, 1, 96) == T("1e96")
+        @test T(1, 1, -101) == nextfloat(T(0))
+        @test T(1, 10, -102) == nextfloat(T(0))
+        @test_throws InexactError T(1, 1, -102)
+        @test_throws InexactError T(1, 11, -102)
         @test eps(Dec32) == parse(Dec32, "1e-6")
         @test floatmax(Dec32) == parse(Dec32, "+9999999E+90")
         @test bswap(Dec32(1.5)) == reinterpret(Dec32, bswap(reinterpret(UInt32, Dec32(1.5))))
     elseif T == Dec64
         @test d"3.2" * d"4.5" == d"14.4"
         @test d64"3.2" * d64"4.5" == d64"14.4"
+        @test T(1, Int64(maxintfloat(T)), 0) == maxintfloat(T)
+        @test T(1, Int64(maxintfloat(T) * 100), -2) == maxintfloat(T)
+        @test T(1, Int64(maxintfloat(T) - 1), 369) == floatmax(T)
+        @test_throws InexactError T(1, Int64(maxintfloat(T)), 369)
+        @test_throws InexactError T(1, Int64(maxintfloat(T)) + 1, 0)
+        @test T(1, 1, 384) == T("1e384")
+        @test T(1, 1, -398) == nextfloat(T(0))
+        @test T(1, 10, -399) == nextfloat(T(0))
+        @test_throws InexactError T(1, 1, -399)
+        @test_throws InexactError T(1, 11, -399)
         @test eps(Dec64) == parse(Dec64, "1e-15")
         @test floatmax(Dec64) == parse(Dec64, "+9999999999999999E+369")
         @test bswap(Dec64(1.5)) == reinterpret(Dec64, bswap(reinterpret(UInt64, Dec64(1.5))))
     else
         @test d128"3.2" * d128"4.5" == d128"14.4"
         @test eps(Dec128) == parse(Dec128, "1e-33")
+        @test T(1, 10000000000000000000000000000000000, 0) == maxintfloat(T)
+        @test T(1, 10000000000000000000000000000000000 * 100, -2) == maxintfloat(T)
+        @test T(1, 10000000000000000000000000000000000 - 1, 6111) == floatmax(T)
+        @test_throws InexactError T(1, 10000000000000000000000000000000000, 6111)
+        @test_throws InexactError T(1, 10000000000000000000000000000000000 + 1, 0)
+        @test T(1, 1, 6144) == T("1e6144")
+        @test T(1, 1, -6176) == nextfloat(T(0))
+        @test T(1, 10, -6177) == nextfloat(T(0))
+        @test_throws InexactError T(1, 1, -6177)
+        @test_throws InexactError T(1, 11, -6177)
         @test floatmax(Dec128) == parse(Dec128, "+9999999999999999999999999999999999E+6111")
         @test bswap(Dec128(1.5)) == reinterpret(Dec128, bswap(reinterpret(UInt128, Dec128(1.5))))
     end
@@ -74,6 +104,17 @@ for T in (Dec32, Dec64, Dec128)
     @test T("0.9999999999999999999999999999999999999999", RoundUp) == T(1)
     @test T("0.9999999999999999999999999999999999999999", RoundDown) == prevfloat(T(1))
 
+    @test T(0, 0, 0) == T(0)
+    @test T(1, 0, 10) == T(0)
+    @test isequal(T(-1, 0, 0), T(-0.0))
+    @test T(1, 125, -2) == T(1.25)
+    @test T(-1, 500, -2) == T(-5)
+    @test T(1, 5, 2) == T(500)
+    @test_throws DomainError T(0, 1, 0)
+    @test_throws DomainError T(2, 1, 0)
+    @test T(125, -2) == T(1.25)
+    @test T(-125, -2) == T(-1.25)
+
     io = IOBuffer()
     show(io, T("NaN")); @test String(take!(io)) == "NaN"
     show(io, T("Inf")); @test String(take!(io)) == "Inf"